GENERAL GLOSSARY

Action: Breech mechanism of a firearm, by which it is loaded and unloaded, and which houses most of the moving parts.

Airgun: Not a firearm but a gun that uses compressed air or CO2 to propel a projectile. Examples: BB gun, pellet gun, CO2 gun.

Ammunition: This generally refers to the assembled components of complete cartridges or rounds i.e., a case or shell holding a primer, a charge of propellant (gunpowder) and a projectile (bullets in the case of handguns and rifles, multiple pellets or single slugs in shotguns). Sometimes called “fixed ammunition” to differentiate from components inserted separately in muzzle loaders.

Antique: By federal definition, a firearm manufactured prior to 1899 or a firearm for which ammunition is not generally available or a firearm incapable of firing fixed ammunition.

Anvil: In a primer or cartridge case a fixed point which the priming mixture is crushed, and thereby detonated by the action of the firing pin.

Armour-piercing Ammunition: By federal definition, “a projectile or projectile core which may be used in a handgun and which is constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium. Such term does not include shotgun shot required by… game regulations for hunting purposes, a frangible projectile designed for target shooting, a projectile which the Secretary finds is primarily intended to be used for sporting purposes, or any other projectile or projectile core which the Secretary finds is intended to be used for industrial purposes, including a charge used in an oil and gas well perforating device.”

Assault Rifles: Class of Rifle generally characterised by the use of a short cartridge and the ability to fire either single shots or short bursts.

Automatic: A firearm designed to feed cartridges, fire them, eject their empty cases and repeat this cycle as long as the trigger is depressed and cartridges remain in the feed system. Examples: machine guns, submachine guns, selective-fire rifles, including true assault rifles.

Automatic Pistol: As commonly used, a pistol which on the pressure of the trigger, will fire and re-load ready to fire the next shot. This is, strictly speaking, a self-loading pistol, and the term ‘automatic’ should only be applied to those pistols ( and other firearms) which will fire and continue to reload and fire so long as the trigger is pressed and there is ammunition available- e.g. machine guns. Automatic pistols can be divided into broad classes, those with locked breeches and those without, the latter being called ‘blowback’

Back Strap: The rear portion of that part of a handgun frame to which the stocks are attached.

Ball: Originally a spherical projectile, now generally a fully jacketed bullet of cylindrical profile with round or pointed nose. Most commonly used in military terminology.

Ballistics:  The science of moving projectiles.

Barleycorn: & Bead : Are two forms of foresight used with rifles.

Barrel: The part’s of a firearm through which passes the bullet or shot, travelling from breech to muzzle.

Base Wad: A compressed paper filler inside the head of the shot shell, used to keep the powder in position in front of the flashing end of the primer.

Battery: The metal arm of a flintlock mechanism against which the flint strikes to create sparks in the flash pan.

Battery Cup: A small metal cup, inserted in the head of the shell or cartridge; in which the cap (primer) is seated.

Beavertail: The forearm or fore-end grip of a firearm which is made wider than standard.

Belted Cartridge: A narrow band around the base of the cartridge case just forward of the  extraction rebate, of which the forwards edge of this band is the place where chamber head space is calculated from.

Black Powder: A mixture of charcoal, sulphur and saltpetre used as a Propellent. Gives off much white smoke when burned.

Blank Cartridge: A round loaded with black powder or a special smokeless powder but lacking a projectile. Used mainly in starting races, theatrical productions, troop exercises and in training dogs.

Blow Back: Is said to occur on firing when gas escapes to the rear, between the cartridge and the sides of the cartridge chamber.

Blow Back System: Operation of an automatic firearm in which the breech block or bolt is not physically locked to the barrel. On firing, the explosion pressure in the chamber causes the cartridge case to be expelled rearwards, where it impinges on the face of the bolt or block and drives it to the rear.

Blow Forward: System of operation of an automatic arm analogous to blowback but in which the breech block is anchored to the firearm and cannot move. The chamber pressure causes the barrel to move forward away from the breech block due to the cartridge case being forced back and the bullet and barrel moving forward.

Bolt Action: Form of breech closure performed by moving in the prolongation of the firearms barrel axis. A  turnbolt in which the bolt is manually pushed forward and then rotated in order to lock by means of angular lugs.

Bolt (Cylinder Stop): A moveable stud protruding through a revolver frame into a notch in the cylinder to hold said cylinder in alignment with a barrel.

Bore: is the interior of the barrel between the front end of the chamber and the muzzle. This term is also sometimes used to denote the calibre.

Bore Diameter:  In rifled arms the diametrical measurement between tops of lands.

Box Magazine: Form of ammunition dispenser which takes the form of a metallic box, either detachable from the weapon and held in a magazine housing or actually forming part of the firearms body. Inside the box is a follower or platform a plate shaped to place pressure on the ammunition contained in the box, this pressure being sustained by a spring.. The magazine may be in a single or double column. The design of the open end of the magazine, the feed lips position the topmost round to align it with the bolt or breech block.

Brass: A synonym for expended metallic cartridge cases.

Breech: The barrel is usually attached to the breech of a firearm. The cartridge is inserted into the breech and locked into place.

Breech Bolt: The part in the breech that controls the thrust of the explosion when the cartridge is detonated.

Bullet: The projectile only, not the cartridge case.

Caliber: Bore or grove diameter expressed in decimals of an inch, other wise in the metric system.

Cam: Is a disc, curved surface, or groove, employed to convert a rotating into a reciprocating motion, or to change the direction of a body in motion.

Cannelure: Circumferential groove pressed or cast in a bullet, generally to allow crimping the case to the bullet. Also a groove in a case to provide a seat for the bullet.

Caplock:. Part of a Muzzle-loading Gun whose ignition system employs a percussion cap, a small metal cup containing a detonating mixture. This cup placed on a “nipple” transmits flame to the powder charge when struck by the guns hammer.

Cap, Primer: The cup in a cartridge case that contains the priming compound which detonates the powder.

Carbine: A short rifle usually for use by cavalry, artillery or others whose primary task is not infantry and need a firearm for self defence.

Cartridge:  A complete round of ammunition, made up of a cartridge case, primer, bullet (or Shot) and powder. This term derived from the French word cartouche, a roll or case of paper containing powder and shot. Since the arrival of metal cartridges, it contains brass or copper case, the powder charge, the primer and the projectile. It is also used in describing shotshells for shotguns, although these contain numerous pellets and not a bullet.

Cartridge Head Space:. Critical dimension in the assembly of a firearm. It is basically the distance between the face of the bolt or breech block and in the base of the cartridge case and is measured in tens of thousands of an inch. If head space is excessive the cartridge case will be able to move out of the chamber when fired and may burst or expand the firearm. If the head space is insufficient the bolt or breech block may be prevented from locking.]

Cartridge Case: Commonly, the brass, steel or copper envelope that contains powder, primer and projectile (shot), but applicable to shot-shells and even  plastic cases.

Case Rim (flange): The thin circular portion of a cartridge case gripped by the extractor to remove it from the chamber.

Centre-fire:  Cartridges those ignited by means of (generally) a separate and replaceable primer located centrally in the head of the case.

Chamber: Enlarged and specially shaped portion of the barrel at its rear end, into which the cartridge is placed prior to firing. The chamber holds  the cartridge and by its lead or blending in to the rifled bore, directs the bullet into the rifling in proper alignment.

Chamber Cast: An impression of a gun chamber obtained by filling the chamber with a molten or liquid material which hardens without significant shrinkage.

Charger: Is a holder which contains a (usually 5) cartridges, for the magazine of a rifle. On loading, the cartridges are swept out of the charger into the magazine.

Choke: The constriction in the muzzle end of a shotgun barrel by means of which control is exerted upon the shot charge in order to throw it’s pellets into a definite area of predetermined concentration.

Clip: Is a holder which contains a (usually 5) cartridges for the magazine of a rifle. On loading, the clip and cartridges are inserted into the magazine; the clip drops out of the bottom of the magazine when empty.

Comb: The upper edge of the firearm stock where the cheek normally rests.

Compensator: Device screwed to the muzzle of a firearm or formed integrally with the barrel or jacket, which deflects some of the emergent gas upwards. This tends to drive the muzzle downwards and counters the tendency for the muzzle to rise during firing due to the axis of thrust being above the point of resistance.

Cone: The slope of the forward end of the chamber of a rifles or shotgun which decreases the chamber diameter to bore diameter. Also called Forcing Cone.
Compound Bullet: Is one composed of a lead core with a thin envelope or jacket of hard metal covering its nose and generally its sides.

Cop-killer Bullet: An inflammatory phrase having neither historical basis nor legal or technical meanings.

Cordite: A British form of nitro-cellulose/nitroglycerine propellant extruded in strings or rods the length of the cartridge powder space. Considered highly erosive to barrels.

Corrosion: The eating away of the metal parts of a firearm due to rusting or oxidization or from the corrosive salts deposited from the powder or primer.

Crane (yoke): In a solid-frame, slide-swing revolver, that part which is pivoted to the frame, (receiver) and carries the cylinder.

Creep: The amount of crawl or drag in a trigger before it lets go of the sear, instead of a short snappy let off.

Crimp: The bending inward of the case mouth perimeter, in order to grip and hold the bullet, or to keep the shot in a paper case intact.

Cylinder: In a revolver, a cartridge container that rotates (generally) around as axis parallel to and below the barrel.

Cylinder latch: A part, usually actuated by one’s thumb, to disengage the cylinder of a revolver so the arm may be opened for loading.

Decapping: Punching out or otherwise removing a fired primer from a cartridge case.

Dent Oil: An inward depression in a cartridge case caused by lubricant trapped between it and the resizing size die.

Delayed Blow back:. Mechanism used in automatic or self loading firearm in which the breech block or bolt is not positively locked to the barrel for the entire period of the bullets travel up the bore and until the chamber pressure has dropped. It is basically a blowback firearm in which some means of slowing down the opening movement of the bolt has been employed.

Density, Loading: A percentage value indicating the portion of the cartridge case volume filled by the propellant charge.

Derringer: A small single-shot or multi-barrelled (rarely more than two) pocket pistol.
 
Detonate: To explode with great violence. It is generally associated with high explosives e.g. TNT, dynamite, etc., and not with the relatively slow-burning smokeless gunpowders that are classed as propellants.

Disconnector: A mechanism of a self-loading firearm which disconnects the trigger from the remainder of the mechanism as soon as the shot is fired and does not re-connect it until the firer positively releases the trigger. This prevents the gun from firing more than one shot for more than one pressure of the trigger.

Double Action: A mechanism for a pistol which offers the firer two methods of discharging the shot; either he may pull back the hammer to the full cock position and then release it by pressure to the trigger. Or he may by pulling the trigger alone raise the hammer to full cock and then release it with the trigger.

Double Trigger: This expression has two meanings:-
1. A mechanism for revolvers in which two triggers are provided, one to cock the hammer and the other to release it.
2. A mechanism used with a firearm where one trigger is provided for firing single shots and another trigger for automatic fire.

Die, Resizing: A cartridge-case-shaped cavity in a block of metal into which the case is pressed to be reduced to acceptable shape dimensions.

Discharge: Ignition of the priming compound, which burns the powder and send the bullet on its flight.

Drift: Is the lateral motion of the bullet, due to its spin and the resistance of the air.

Dum-dum Bullet: A British military bullet developed in India`s Dum-Dum Arsenal and used on India`s North West Frontier and in the Sudan in 1897 and 1898. It was a jacketed .303 cal. British bullet with the jacket nose left open to expose the lead core in the hope of increasing effectiveness. Improvement was not pursued, for the Hague Convention of 1899 (not the Geneva Convention of 1925, which dealt largely with gas warfare) outlawed such bullets for warfare. Often “dum-dum” is misused as a term for any soft-nosed or hollow- pointed hunting bullet.

Ejector Rod: A rod protruding under the barrel of a revolver which is pressed rearward to extract the eject cases from the cylinder.

Ejector: Firearm part which physically expels the cartridge case from the firearm after the shot has been fired. In most cases it is simple a protuberance of metal so placed that the bolt or breechblock will carry the fired case up against it causing the case to knocked from the firearm and out of the ejection port.

Elevation:  The term used to designate the vertical movement of an adjustable rear sight. Which is used to change the angle of the rifle barrel, effecting the elevation of the fired projectile.

Energy:  In bullets, the amount of work done, at given ranges, expressed in foot pounds.

Engraving: When a bullet is driven into the rifling and the lands cut or ‘engrave’ into the bullet surface.

Erosion: More or less gradual wearing away of rifling by combustion gas, heat and bullet friction.

Expander: A plug or ball forced into a cartridge case mouth to produce the correct diameter to permit seating and holding a bullet.

Exploding Bullet: A projectile containing an explosive component that acts on contact with the target. Seldom found and generally ineffective as such bullets lack the penetration necessary for defence or hunting.

Explosive: Any substance (TNT, etc.) that, through chemical reaction, detonates or violently changes to gas with accompanying heat and pressure. Smokeless powder, by comparison, deflagrates (burns relatively slowly) and depends on its confinement in a gun`s cartridge case and chamber for its potential as a propellant to be realized.

Extractor: A component of a firearm which is generally attached to the bolt or breechblock and which pulls the empty cartridge case out of the chamber and presents it to the ejector.

Firearm: A rifle, shotgun or handgun using gunpowder as a propellant. By federal definition, under the 1968 Gun Control Act, antiques are excepted. Under the National Firearms Act, the word designates machine guns, etc. Airguns are not firearms.

Fire-Form: To shape a cartridge case intimately to the chamber by firing it therein.

Figure of Merit: Of a group of shot is the average distance of the shots from the point of mean impact; the latter is the centre of the group, and is at the intersection of the lines of mean vertical height, and mean horizontal position.

Firing Pin: A firing mechanism actuated by a hammer or spring, which strikes the primer and fires the cartridge.

Fixed Ammunition: A complete cartridge of several obsolete types and of today’s rimfire and centre-fire versions.

Flame Temperature: The nominal temperature produced inside a cartridge case during combustion of the propellant.

Flash Hider/Flash Suppressor: A muzzle attachment intended to reduce visible muzzle flash caused by the burning propellant.

Flash Hole: The small hole connecting primer pocket to interior of case, through which primer flame passes.

Fluted Chamber: A chamber of a firearm which has thin grooves cut longitudinally through out most or all of the length and which extends past the neck of the cartridge case when loaded. In such a chamber, when the cartridge is fired a proportion of the propelling gas passes back along the flutes and thus equalises the pressure inside and outside the fired case, literally floating the case on a layer of gas. This system is mainly used in blowback firearms to prevent the cartridge case from sticking in the chamber.

Fluxing: Stirring and adding grease to molten lead to improve its casting qualities and float out impurities.

Flintlock: Used of a muzzle loading gun fired by means of a piece of flint, held in the hammer or “cock” jaws, striking against a steel “frizzen”. Incandescent particles of steel scraped from the frizzen fall into a “pan” holding powder. This ignited powder flames through the “touch-hole”, thus firing the main charge.

Foil: In reference to a primer, the thin disc of waterproof material pressed over the priming compound and lacquered in place to exclude moisture.

Follower: A metal platform in a clip or magazine that pushes the cartridges upward at the proper angle for feeding into the chamber.

Fore-end: The forward portion of the wood stock under the barrel serving as a fore grip on the firearm.

Front strap: The front portion of the part of a handgun frame to which stocks are attached, sometimes including the trigger guard.

F.P.S.: Feet Per Second, used in giving bullet velocities and calculating the speed of moving projectiles of any description.

Gauge: Shotgun-Unit of measure for shotguns bore diameters, determined by the number of solid lead balls of the bore diameter obtainable from one pound of lead. i.e. 12 Gauge=12 balls to the pound.

Gas Check: A cup (usually copper) used on the base of a lead bullet to protect it from hot powder gases.

Gas Operation: One of the basic methods of operating an automatic or self-loading firearm. A portion of the propelling gas is trapped from the barrel via a port and directed to a cylinder in which a piston moves. The pressure of the gas drives the piston back and this movement is then applied to the breechblock so as to open the breech and reload the firearm.

Gliding Metal: A copper-zinc alloy used as bullet jacket material; usually 5% to 10% zinc.

Grain, Powder: Commonly and confusingly used to mean individual kernels or particles of propellant. Particularly confusing since propellant is weighed in grains avoirdupois.

Grooves: Spiral cuts in a bore which cause the bullet to spin as it travels down the barrel.

Groove Diameter: In rifled barrels, the diametrical measurement between bottoms of grooves.

Groove lubricating: A groove around a bullet to contain lubricant.

Group: Number of shots fired into a target (number and range optional), usually with one sight setting.

Grip: The small part of the stock gripped by the trigger hand when firing the firearm.

Grip Safety: A lever or plunger let into the grip of a pistol or other firearm in such a manner as to positively lock the bolt or hammer or trigger unless the firearm is held is held properly and the grip is consciously depressed. Prevents the firearm from being accidentally discharged if dropped or mis- handled.

Gun: The British restrict the term in portable arms to shotguns. Here it is properly used for rifles, shotguns, handguns and airguns, as well as cannon.

Gunpowder: Chemical substances of various compositions, particle sizes, shapes and colors that, on ignition, serve as a propellant. Ignited smokeless powder emits minimal quantities of smoke from a gun’s muzzle; the older black powder emits relatively large quantities of whitish smoke.

Half Jacket: A type of handgun bullets in which a thin, soft copper alloy jacket covers only the surface in contact with the bore.

Hammer: ‘Striker’, Striking  component of the firing mechanism energized by the hammer or main spring and released by the sear. The hammer drives the firing pin against the primer , thus igniting the cartridge powder charge.

Hammerless:. A confusing term which sometimes means that the hammer cannot be seen . Strictly speaking, it should mean what it says and imply that the firing pin of the cartridge is done by an axial striker or firing pin/striker, which in it self is a hammer, but in practice the word is often applied to shotguns and revolvers which in fact do have hammers concealed within the frame.

Hand: A finger-like part attached to hammer or trigger that rotates the cylinder of a revolver when the arm is cocked.

Handgun: Synonym for pistol.

Hang-fire: A cartridge which fires as long as several seconds after firing pin strikes primer.

Head space: For rimmed cartridges, the distance from the face of the breechblock to the barrel seat for the forward surface of the case rim. For a rimless bottleneck cartridge, the distance from the face of the breechblock to a predetermined point on the shoulder of the chamber. For rimless straight cartridges, the distance from the face of the breechblock to the shoulder or ledge in the chamber.

High-Capacity Magazine: An inexact, non-technical term indicating a magazine holding more rounds than might be considered “average.”

Hinge Frame: Type of revolver in which the barrel and cylinder form a moveable unit which is hinged to the butt frame by a pivot pin at the front edge of it. When closed two sections are locked together by some form of catch on the top strap locking the breech, cylinder and barrel to the butt.

Hollow Point: A type of bullet containing a cavity in its point to promote expansion upon impact.

Jacket: The envelope enclosing the core of a bullet.

Jump:  Is the angle made by the axis of the barrel before firing, with the tangent to the trajectory at the muzzle.

Lands: That portion of the bore remaining after the rifling or grooves have been cut.

Leading or Metallic Fouling: Consist of the particles of metal detached from the surface of lead or compound bullets respectively, which adhere to the surface of the bore.

Line of Fire: Is a continuation of the axis of the bore at the muzzle, at the instant that the bullet leaves the barrel; in other words it is a tangent to the trajectory at the muzzle.

Line of Sight: Is the straight line passing through the sights and the point aimed at.

Leade (Lead): The beginning of the rifling where the lands are tapered in thickness to provide clearance for the bullet or,

Lead: (pronounced as the verb to lead) Is the conical part of the bore just in front of the cartridge chamber. It forms a funnel to lead the bullet into the rifling.

Leading: Lead deposited on bore by bullets passing through.

Lever Action: A rifle breech action operated by a hand lever which lies beneath the firearm and generally forms an extension of the trigger guard.

Lock: The working  mechanism of a Rifle Pistols or Shotgun that locks in and contains the pressure from the exploding powder charge. This mechanism usually contains the locking mechanism, the feeding mechanism, the safety mechanisms, the extraction mechanism, the ejection mechanism and the firing mechanism.

Lock Speed: The time between the trigger disengaging the primary sear and the detonation of the primer in the cartridge case.

Long Recoil System: Operation of an automatic or self-loading firearm in which the barrel and breechblock are securely locked together at the instant of firing and then recoil, still locked, for a distance greater than the length of a complete unfired cartridge case. Having so recoiled the breech is unlocked and the breech block is held fast while the barrel returns to battery.

Machine Gun: A firearm of military significance, often crew-served, that on trigger depression automatically feeds and fires cartridges of rifle size or greater. Civilian ownership in the U.S. has been heavily curtailed and federally regulated since 1934.

Magazine Safety: A form of safety device used with automatic pistols in which the pistol cannot be fired if the magazine is removed.

Magazine: Device or reservoir to hold extra cartridges, of many types and names. “Clip” once reserved for the metal strip from which cartridges are fed into a magazine well, now refers to separate, detachable magazines also, as with those for self-loading pistols.

Magnum: A term indicating a relatively heavily loaded metallic cartridge or shot shell and, by extension, a gun safely constructed to fire it.

Main Spring: The spring in a pistol which propels the hammer.

Matchlock: An early form of firearm in which the priming charge was ignited by a cord or “match” of slow-burning material.

Mid-Range. Usually used with reference to trajectory, designating a point midway between  the muzzle of the barrel and the target or point of impact.

Multi-barrelled: A gun with more than one barrel, the most common being the double-barrelled shotgun.
 
Mushroomed Bullet: A description of a bullet whose forward diameter has expanded after penetration.

Muzzle: End of barrel opposite to breech; point from which bullet or shot leaves barrel.

Muzzle Brake: An attachment to or integral part of the barrel intended to trap and divert expanding gasses and reduce recoil.

Muzzle Loader: The earliest type of gun, now also popular as modern-made replicas, in which blackpowder and projectile(s) are separately loaded in through the muzzle. The term is often applied to cap-and-ball revolvers where the loading is done not actually through the muzzle but through the open ends of the cylinder`s chambers.

Muzzle Pressure: Gas pressure in a gun barrel at the instant the bullet exits the muzzle.

M.E.: Muzzle energy .

M.V.: Muzzle Velocity.

Muzzle Velocity: Is the greatest velocity of the bullet, it is attained a little beyond the muzzle of the rifle. It is written for short M.V. Initial velocity is perhaps a preferable term.
Nipple: On muzzle-loading arms, the small metal cone at the rear of the barrel (or cylinder) through which the flame from the percussion cap passes to ignite the powder charge.

Open Frame: Type of revolver in which the the barrel section is attached to the bottom of the butt frame, and there is no top strap passing from the barrel to the standing breech.

Pan: Hold the ignition or flash powder in a flintlock.

Pattern: Designates the distribution of shot fired from a shotgun, usually from comparative purposes, measured as a standard at 40 yards and within a 30 inch circle.

Pellet Gun: A rifle or pistol using compressed air or CO2 to propel a skirted pellet as opposed to a spherical BB. Not a firearm.
 
Pellets: Small spherical projectiles loaded in shot shells and more often called “shot.” Also the skirted projectiles used in pellet guns

Percussion:  While almost all modern firearms are fired by the application of a percussive blow to a sensitive cap, this term is applied solely to firearms fired by the use of a separate cap placed on a nipple communicating with the chamber and thus implying a black powder muzzle loading firearm.

Percussion Cap: Small metallic cup containing fulminating material that explodes when struck by gun’s hammer. See nipple.

Pistol: Reputedly derived from Pistoia, an early gun making centre in Italy. Any small, conciliable, short-barrelled hand weapon, generally not a revolver.

Pistol Grip: The handle of a handgun or protrusion on the butt stock or fore-end of a shoulder-operated gun that resembles the grip or handle of a handgun. A “semi-pistol grip” is one less pronounced than normal; a “vertical pistol grip” is more pronounced than normal

Plinking: Informal shooting at any of a variety of inanimate targets. The most often practised shooting sport in this country.

Port Pressure: Gas pressure in a firearm barrel at the instant the bullet passes over a gas port therein.

Powder; ball: Smokeless nitrocellulose propellent formed into small balls in emulsion. Often balls are flattened to oblate spheroid forms by rolling.

Powder: flake: Nitrocellulose propellant rolled into thin sheets, then cut into square or diamond-shaped individual flakes; not perforated. Typical of European propellants.

Powder: stick (extruded; IMR-type; rod): Nitrocellulose propellant extruded in round or string form, usually containing a central perforation, then cut to length to form short individual cylindrical granules.

Pressure: The gas pressure generated in a cartridge on its being fired, usually expressed in (greatest) pounds per square inch (P.S.I)

Primer: In a centre-fire cartridge the small cup, containing a detonating mixture, which is seated in a recess in the base of the case.

Primer, (Corrosive): A primer containing any compound which produces hygroscopic residue which tends to promote rapid rusting of barrels.

Primer, (Extrusion): When the soft metal of the primer cup flows back under pressure into space between firing pin and bolt or breech face, but does not rupture.

Primer, (Mercuric): A primer containing fulminate of mercury, the combustion products of which amalgamate with and embrittle case brass.

Primer, (Pierced or Perforated): When a disc of cup metal is blown out into the firing pin hole in the breech; usually caused by excessive firing pin clearance and protrusion combined with high chamber pressure.

Primary Extraction: Is the first backward motion or loosening of the cartridge in the chamber, effected while disengaging the lugs of the bolt from their seating.

Propellant: Powder: The chemical compound serving as the fuel in the cartridge. Generally classed as either black or smokeless.

Pyrodex: A trade name for a black powder substitute, the only such safe substitute known at this time. 

Range: Is the distance from the muzzle of the rifle to the second intersection of the line of sight by the trajectory.

Rachet: A notched ring centred in the rear of a revolver cylinder and engaged by the hand to turn said cylinder.

Rebated-Head: Form of cartridge case in which the flange provided for extraction is of smaller diameter than the adjacent base of the case.

Receiver: A part of a firearm  which receives the barrel, the ammunition the stock and other parts into it.

Recoil Operation System: Operation of a self loading or automatic firearm which relies on the recoiling of the barrel, due to firing, to generate the necessary power to operate the reloading cycle.

Recoil Spring: That spring in an automatic or self loading firearm which returns the bolt or breechblock after recoil; sometimes known as the return spring.

Recoil: the backward thrust of a gun caused by the reaction to the powder gases pushing the bullet forward.

Recoil Shield: That portion of a revolver frame which supports the heads of the cartridges to prevent their moving out of the cylinder.

Revolver: A repeating firearm in which the barrel is fixed and the ammunition is contained in a rotary cylinder behind it, with a mechanism which will index the cylinder round so as to present a fresh cartridge to the barrel for each pressure of the trigger.

Rifle: A shoulder gun with rifled bore.
 
Rifling: Spiral grooves cut into the bore of a firearm so as to impart rotary motion to the bullet during its flight. The object is to gyroscopically stabilise the bullets flight so that it travels point foremost, retaining its accuracy.

Rimfire: A type of cartridge which the rear part of the case is formed into a rim by pressing, so as to leave the rim area hollow. This is then filled with a sensitive percussion composition, and the body of the case filled with propellent powder, the bullet then being seated on the top. When loaded the rim rests against the face of the chamber, the firing pin is arranged to strike on the rim and thus nip the composition between the pin and the chamber, producing sufficient friction to initiate the propellent.

Rim: The projecting edge of the base or “head” of certain cartridges.

Round: Synonym for a cartridge.

Rupture (Separation) Case: A failure wherein cartridge case separates in two parts around its perimeter just ahead of the rim or extraction groove.

Sabot: A lightweight carrier surrounding a heavier projectile of reduced caliber, allowing a firearm to shoot ammunition for which it is not chambered. For example, a hunter could use his .30-30 deer rifle to shoot small game with .22 center-fire bullets.

Safety Lever (Block): In modern revolvers a part that moves to prevent the hammer from going fully forward unless the trigger is deliberately pulled fully to the rear.

Sawed-off Shotgun (Rifle): Common term for federally restricted “short-barrelled shotgun (rifle)” i.e. a conventional shotgun with barrel less than 18″ (rifle less than 16″) or overall length less than 26.”

Sear: A mechanism linked to the trigger which engages with the hammer or striker against its own spring pressure and when pulled/pushed clear by the trigger mechanism allows firing

Selector: Device which operates the disconnector.

Selective-Fire: A firearm’s ability to be fired fully automatically, semi-automatically or, in some cases, in burst-fire mode at the option of the firer.

Self-Cocking: A complex group of revolver mechanisms where pressure on the trigger cocks the hammer and then releases it to fire.  Though normally associated with revolvers, can also be used on automatic pistols with an axial striker. 

Self -Loading: Any firearm which, for a single pressure of the trigger, fires and then by its own agency re-loads. The trigger must then be released to fire the next round. The commonly defined automatic pistol is in fact a self-loader.

Semi-Automatic: A firearm designed to fire a single cartridge, eject the empty case and reload the chamber each time the trigger is pulled.

Separation: Is a circumferential fracture of the cartridge case on firing. It may be either partial or complete; in the latter case the front part of the cartridge case is left in the chamber when extraction takes place.

Set Trigger: Form of trigger mechanism found on target firearms. As well as the firing trigger there is usually a second trigger or stud or lever of some sort which is operated first so as to cock, or set the trigger mechanism and set the firing trigger so that a very light pressure on it will discharge the firearm.. The actual firing trigger is not called upon to raise hammers or do any other heavy work for which stiff springs are needed all this is done by the setting trigger.

Sheathed Trigger: Form of trigger commonly found on American revolvers of the 1860-1880 period, and occasional on European revolvers. The frame of the pistol has an extended spur or sheath; when the hammer is cocked ready to fire, the trigger is forced out so that it can be pressed. Obviously restricted to single action weapons. Also known as a ‘stud’ trigger.

Shotgun: A shoulder gun with smooth-bored barrel(s) primarily intended for firing multiple small, round projectiles, (shot, birdshot, pellets), larger shot (buck shot), single round balls (pumpkin balls) and cylindrical slugs. Some shotgun barrels have rifling to give better accuracy with slugs or greater pattern spread to birdshot.

Shotshell: The cartridge for a shotgun. It is also called a “shell,” and its body may be of metal or plastic or of plastic or paper with a metal head. Small shotshells are also made for rifles and handguns and are often used for vermin control.

Shoulder: The sloping portion of a bottleneck cartridge case that joins the body and neck.

Silencer: Device attached to the muzzle of a firearm in order to reduce the noise of discharge. The first practical silencer was invented by Maxim. Its usual form is a large cylinder with metal plates pierced to permit the passage of the bullet. The emerging gases are caught by these plates and deflected around the the inside of the casing, so that by the the time they emerge their velocity is reduced to a point where they do not generate sufficient disturbance of air to cause noise.

Single Action: Term used to describe a revolver mechanism in which the hammer must be pulled back and cocked by hand, after which the trigger can be pressed to release the hammer and fire the pistol.

Slide Action: A more formal term for what is popularly called a ‘pump action’ a reciprocating fore-end on a shotgun or a rifle which, when pulled back, opens and closes the breech.

Sizing: Hand loading cartridges, sizing (or resizing) brings the fired cartridge case back to the (full or partial) dimensions of the new or unfired case. Bullets are also sized.

Smokeless Powder: Propellent powder for cartridges based upon nitrocellulose, with various additives. It is not entirely smokeless, but in comparison with to gunpowder or black powder the appellation is appropriate. It is considerably more resistant to damp, more powerful for a given bulk, more consistent and gives less fouling in the bore. Usually made by nitrating and otherwise chemically treating purified cotton waste.

Snub-Nosed: Descriptive of (usually) a revolver with an unusually short barrel.

S.P.:  Soft Point: A term applied to bullets with partial metal jacketing, having some lead exposed at the point.

Solid Frame: Form of revolver construction in which the frame is in one piece, with a rectangular aperture for the cylinder. It follows that to empty and load the cylinder either there must be a prepared ‘gate’ at one side through which the chambers can be reached one at a time, or the cylinder must be removed in some way. Current manufactures, almost all makers use a solid frame and mount the cylinder on a crane so that it can be swung out of the frame for loading.

Spent Case Projection: Another way of describing a ‘blow back’ action since the breech block is projected by the chamber pressure acting via the spent cartridge case.

Sprue (sprew): The excess portion of a cast bullet filling the funnel-like area through which molten lead enters the hold. Cut off before bullet is used.

Sprue-Cutter (plate): The pivoted plate on top of a bullet mould through which a bullet is pressed and confined by one or more shaped punches to give it shape and dimensions desired.

Squeezebore: Type of rifle barrel in which the calibre is suddenly reduced and then continues at this reduced figure to the muzzle. When used with deformable bullets, this system boosts the muzzle velocity since it reduces the area of the bullet base presented to the pressure of the propellent gas. If for a given pressure of gas, the base is reduced in area, then the pressure per unit of area must increase, and this increases the velocity. It has been used experimentally but never in mass production.

Standing Breech:: That part of a revolver frame which is immediately behind the cylinder and acts as resistance to the recoil of the cartridge as it is fired. It is generally either pierced to admit the passage of the firing pin attached to the hammer, or carries a separate firing pin which is struck by the hammer the sides of the standing breech are extended to cover rear surfaces of the cylinder so as to prevent the cartridges from falling out. Or being jarred out by  the recoil of the pistol, and those extended sides are known as the ‘recoil shields’.

Stirrup Latch: Form of latch which holds the two sections of a hinged-frame revolver together. It is in the form of an inverted ‘U’ running up, across and down the side of the of the standing breech and controlled by a thumb lever.

Straight-Pull: Type of bolt action in which instead of lifting the bolt handle so as to rotate the bolt from engagement, the handle is pulled straight back, locking lug rotation being achieved by a cam mechanism.

Striker: Alternative term used for the firing pin of a firearm, when that firing pin is axially mounted and spring propelled, as for instance inside a rifle bolt.

Strip Feed:  System of providing ammunition for machine guns in the form of metal trays or strips into which the cartridges are clipped. The tray is fed into the gun at one side, the cartridges are stripped out and fired, the cases ejected and the empty tray ejected from the other side of the gun.

Stripping: A compound jacketed bullet is said to strip when the lead core is blown through the envelope, generally leaving the latter in the bore. This is also termed a blow through. A lead bullet is said to strip when it is blown out of the bore, across the lands, without following the rifling.

Stock: The wooden part of a firearm to which the barrel and receiver are attached.

Submachine Gun: A submachine gun is a lightweight, one man firearm, capable of automatic fire, firing low powered pistol cartridges and hence having limited range and accuracy in comparison with a machine gun.

Suicide Special: Name coined by American authority Donald B. Webster Jr and used to collectively describe the common single-action sheathed trigger revolvers which flooded the market after the Rollin White patent. Such firearms were made to sell at prices as low as sixty cents apiece.

Tape Primer: System of delivering percussion priming caps to the nipple of a firearm by affixing them to a flexible tape and linking the feeding of the tape to the actuation of the hammer. See Maynard Patents.

Taper Bore: Rifle in which the calibre gradually decreases from the breech to the muzzle. This allows a higher velocity to be attained and the principle is the same as the squeeze bore. The difference is that here the taper is gradual, where as with the squeeze bore the change in calibre takes place over a short section of the bore.. Rifles of this type were tried as sniping rifles by various countries and then in anti tank rifles during the Second World War.

Teflon: Trade name for a synthetic sometimes used to coat hard bullets to protect the rifling. Other synthetics, nylon for instance, have also been used as bullet coatings. None of these soft coatings has any effect on lethality.

Toggle Lock: System of breech locking for a recoil-operated firearms notable the Maxim machine gun and the Parabellum ‘Luger Pistol’. The system requires a barrel with barrel extension; inside the barrel extension is the breech block, and behind this are two arms One is hinged to the breech block, the other is hinged to the barrel extension and the two are linked by a hinge bolt in the middle, thus, breech block-hinge-arm hinge arm hinge barrel extension. When the bolt is closed, the central hinge lies below the  axis of the barrel by a slight amount, so that any pressure on the block tends to force the hinge down, where it is stopped by the surface of the barrel extension. When the firearm fires, therefore the whole unit recoils, the opening action of the block being resisted by the toggle arms lying slightly depressed. If however a ramp on the firearms frame is now arranged so as to kick up the central hinge, all resistance ceases and the breechblock is free to recoil in the barrel extension, folding up the toggle joint as it does so.

Throat, Barrel: That portion of a revolver barrel that is “funnelled” to facilitate entry of the bullet as it passes from cylinder to barrel.

Throat, Cylinder: That portion of a revolver chamber through which the bullet must pass before entering the barrel.

Top Strap: The top portion of a revolver frame passing over the cylinder.

Trajectory: Curved path of bullet in flight, a parabola. The curve described by its centre of gravity in its flight through the air to the first point of impact. The trajectory of a group of shots is the trajectory of the bullet which would strike the point of mean impact. The trajectory of a rifle at any particular range, is the trajectory of a group of shots fired at that range under normal atmospheric conditions, with standard cartridges.

Trigger: Mechanism that disengages the sear nock releasing the hammer, which inturn strikes the priming compound in the cartridge.

Tubular Magazine: Magazine in a repeating firearm , usually a rimfire or a shot gun in which the cartridges are carried end to end in a tube mounted beneath the barrel. Only suited to use with blunt nose bullets, since pointed bullets in contact with the percussion cap of the next cartridge, can fire the cap due to shock of recoil when the gun is fired.

Twist: Pitch of the rifling usually uniform and expressed in turns or part-turns in so many inches. Less common, “progressive” or “gain” twist, usually starting at a rate at breech the becomes progressively faster.

Underlug: On S & W  revolvers an integral protrusion of the barrel which houses the forward portion of the cylinder locking mechanism.

Upset (slug): Wherein a bullet expands radially and is foreshortened by violent acceleration given it by propellant gases. Also accomplished in swaging to increase bullet diameter.

Velocity: Projectile speed, usually measured in feet per second (f,p,s.) At the muzzle and other distances such as 100 yards, 200 yards, etc. Measure of the speed of the bullet. May be defined as muzzle velocity when referring to the speed at which the bullet actually leaves the muzzle; observed velocity, when the speed is determined at some specific point in flight, or remaining velocity, which refers to the speed of the bullets as the end of its flight. Abbreviation for these are M.V  OV and RV respectively, through  European usage prefer V.O. for Muzzle velocity.

Vent: Orifice through the nipple.

Venting: Cutting air-escape grooves in bullet mould block meeting surfaces.

Wad, Base: A fibre (usually) cylindrical plug in the head of a built-up shot shell to provide a seat for the primer, and to bind head and body together.

Wad Column: The entire stack of wads in a shotshell between powder and shot.

Weapon: Webster defines it as “an instrument of offensive or defensive combat.” Thus an automobile, baseball bat, bottle, chair, firearm, fist, pen knife or shovel is a “weapon,” if so used.

Wheel Lock: Used in a muzzle-loading gun fired by means of a piece of flint or tyrites, held in the hammer jaws, which is held over a serrated steel wheel. This wheel, set in motion by a tensioned spring, protrudes through the bottom of the “pan” (wherein powder has been placed) and bears against the flint. Sparks are created, as in the flintlock, and the gun is fired by a flame passing through the touch-hole.

Zero: A firearm is said to be ‘zeroed’ when the sights are adjusted so that the bullet will strike the point of aim at some specified distance. From this ‘zero’ point the sight adjustment mechanism will be able to alter the sight line for different ranges so that the bullet strike still coincides with the aiming point, but unless the sight mechanism is modified to suit the individual shooter, his method of aiming and the ammunition in use, before anything else is done further modifying of the sights will be adding unknowns to unknowns.

Achromatic
A lens classed as achromatic has been formulated to be free of chromatic aberration, which causes colour fringing. An achromatic lens, or achromat, achieves identical focus with light rays of two different colours.

Apochromatic
Apochromatic lenses are corrected to bring all three primary colours to the same focus.

Astigmatism
Aberration in a lens or optical system that makes lines oriented in certain directions less sharply focussed than lines running in other directions. Astigmatism also occurs in the human eye. A typical astigmatic effect would be to see the vertical lines on a sheet of graph paper sharply while seeing the horizontal lines less clearly, or vice versa.

Bell
In scope sights with ends flared to accommodate large-diameter ocular or objective lenses, the oversized lens housings are referred to as bells, as in ocular bell or objective bell.

Binocular Collimation
Regulating the two halves of a binocular for parallelism. If the halves are misaligned, the images they form will not merge into a single, sharply defined viewing image. Severe misalignment causes a perceptible multiple-image effect. Slight misalignment may not be specifically obvious, but will result in eyestrain during prolonged viewing.

Catadioptric Lens
A lens system containing front-surface mirrors in addition to refractive lenses. Catadioptric designs “fold” the light path internally to reduce the overall length of the lens system to a significantly shorter dimension than a conventional design would require for a given focal length. Catadioptric lenses, also called mirror lenses, are sometimes used as compact telephoto camera lenses and are occasionally employed in spotting scopes. They are relatively common in astronomical telescopes.

Centre Focus
Refers to a type of binocular with a central focussing control that adjusts both halves of the binocular simultaneously. In centre-focus binoculars, one ocular lens is individually adjustable for focus while the other is fixed. Initially, the user focuses the fixed-ocular half of the instrument with the central control, then focuses the other half with its independently adjustable ocular. Further focussing requires using only the centre control. Centre focus binoculars are quick and easy to use, but are relatively complex mechanically.

Chromatic Aberration
Occurs when a lens brings different wavelengths (colours) of light to separate and distinct points of focus rather than to a common focus. Depending upon the severity, the effect may range from very slight unsharpness to gross unsharpness with visible colour fringing.

Collimator
An optical device containing a lens system that bends light rays passing through it to make the rays parallel. The lens system is often coupled with a target such as a reticle or, in certain applications, a pinpoint light source. A collimator is used to “trick” another optical device, such as a camera lens, telescope or scope sight, into forming an image of the collimator’s reference target as though it were a distant target rather than a very close one. In the optical industry, collimators are widely used for visually assessing the image-forming characteristics of lenses or lens systems. In the context of sporting firearms, small collimating units, also called boresighters, can be used to regulate a scope sight’s reticle to approximately match a shoulder arm’s bore axis in the relative comfort of shop or home, without making a trip to a firing range. The scope “zero” achieved by careful use of a collimator should be considered simply a rough setting that must be refined by actual test firing.

Coma
Off-axis lens aberration that distorts oblique light rays transmitted by the lens. Coma produces taillike smears on tiny round image details such as points of light. Under high magnification, coma may make tiny points of light resemble miniature comets.

Crosshairs
A cruciform reticle in an optical sight, also commonly referred to as crosswire’s.

Curvature of Field
Off-axis lens aberration that makes light rays come to a focus at different points along a curved, rather than flat, focal plane. When viewing a flat subject, such as a paper target or a brick wall that is perpendicular to the lens axis, curvature of field will make it impossible to obtain sharp focus at the centre and edges of the viewing field simultaneously. When the centre is sharp, the edges will be soft; altering focus to sharpen the edges of the image will blur the centre.

Diaphragm
A mechanical device for reducing the amount of light entering or transmitted by an optical system. In simplest, non-adjustable form, often called a stop or Waterhouse stop, the diaphragm is nothing more than an opaque plate configured to fit in a slot or holder in the lens system, or to attach over a lens. The plate has a hole of the desired size, usually circular, that allows a limited amount of light through the optics. An adjustable diaphragm, such as found in most camera lenses and called an iris diaphragm, consists of several interconnected, overlapping movable metal or composition blades that can be opened and closed concentrically to vary the size of the central aperture. Using a stop or diaphragm to reduce the effective aperture of a viewing system produces two immediately evident effects. First, the brightness is reduced. Second, the depth of field is increased. Depth of field refers to the zone of sharpness from near to far in the observed image. Accessory stops or diaphragms available for some target-model rifle scopes are used to enhance sharpness in depth, which is quite limited with high-magnification optics. Iris diaphragms or interchangeable stops are often used in conjunction with high-precision aperture sights on match rifles to achieve optimum clarity of front sight and target. Handgun shooters who cannot see iron sights clearly without corrective spectacles that render the target unacceptably blurry may manage to sharpen sights and target adequately by placing an accessory small-aperture diaphragm or stop plate over the aiming eye’s eyeglass lens.

Diopter
A measurement unit that expresses the refractive power of a lens. Focussing eyepieces of scope sights and binoculars are sometimes equipped with a scale calibrated in diopters to facilitate returning to a previously determined setting. The corrective power of simple eyeglass lenses is given in diopters. Accessory diopter correction lenses are sometimes available for installation in viewing systems or sights to allow comfortable use while wearing non-prescription shooting glasses.

Distortion
A distorted image falsifies subject contours and/or proportions. Distortion is most easily perceived when viewing subjects of known shape and dimensional relationships. Two common forms of distortion are barrel distortion and pincushion distortion. Barrel distortion makes straight lines appear to bow outward toward the edges of the field. Pincushion distortion makes straight lines appear to bow inward toward the centre of the field. Small amounts of distortion may be tolerable in viewing optics provided the distortion remains fairly unobtrusive, as it generally does not impair overall utility. Nonetheless, the finest viewing optics are virtually free of distortion.

Erector lens
Certain combinations of objective and ocular lenses yield an inverted image. An erector lens incorporated into the system serves to reorient the image right side up. In binoculars and telescopes, prisms are often used to “erect” the image.

Exit Pupil
The exit pupil of an optical viewing system appears as a bright disc of light that may be seen by looking into the ocular lens from about 10″ with the instrument aimed at a light source (not the sun!) or a bright background. Within certain limits, the larger the exit pupil, the brighter the view through the optical system. You can calculate the aperture of the exit pupil in millimetres by dividing the effective diameter of the objective lens in millimetres by the magnification of the instrument. An exit pupil aperture as small as 2 mm is large enough for easy viewing in good daylight conditions. An exit pupil diameter of approximately 7 mm is large enough for darker environments or evening use. As the pupil of a normal human eye cannot open larger than about 7 mm, there is little or no practical brightness advantage to designing ordinary viewing instruments with excessively large exit pupils.

Eyepiece
The lens or lens group through which the user of an optical instrument views the image. The term eyepiece is often used interchangeably with “ocular” or “ocular lens,” but may also refer to the physical rim or mount flange that contains the outermost lens of the ocular. The context in which the word occurs normally reveals the meaning.

Eye Relief
The distance between the user’s eye and the ocular lens at which the entire field of view of a scope sight or other optical device is visible simultaneously. Instruments described as having long or extended eye relief allow more than the usual distance between eye and ocular. Long-eye-relief rifle scopes are desirable on rifles that recoil strongly to reduce the likelihood of the ocular striking the shooter’s eye or face. Handgun scopes with extended eye relief provide a full field of view when held at arm’s length. Long-eye-relief spotting scopes and binoculars allow users to see the entire field of view while wearing eyeglasses.

Field of View
The expanse of subject included within the field of an optical system. The measurement is normally taken across the diameter of a circular field and, in the US, expressed, for scope sights, in feet or yards at a subject distance of 100 yards unless otherwise stated. The field of view of binoculars is generally given for 100 or 1000 yards. In countries using the metric system, field of view is commonly expressed in metres at a subject distance of 100 or 1000 metres. Field of view may also be specified in angular terms, as an angle of view. Knowing the angle of view allows calculating the field of view for any subject distance of interest.

Flare
The scattering of non-image-forming light within an optical system, caused by poorly controlled internal reflections from lens surfaces or mechanical components. Flare may be perceived as stray reflections, as a veiling glare or hazy quality that obscures detail in the image, as a loss in image contrast, or as any combination of these phenomena. It is most likely to occur when the field of view includes highly reflective, brightly lighted features or a strong light source. Some target scopes and spotting scopes are equipped with lens shades that may be quite effective in suppressing flare by preventing sunlight from shining directly on the front element of the objective lens in side-lighting or when shooting against the light. The higher the quality of the optical system, the less likely it will be to exhibit flare effects, although no optical system is immune to flare under extreme’ lighting conditions.

Focal Plane
The plane where the image formed by the lens or lens system is in sharp focus. In a camera, the focal plane is the sensitized surface of the film.

Focus
This term may refer to the focal point of a lens, a lens’ focal length, the condition of maximum clarity of an image or the action of adjusting a lens system to yield the clearest and best defined image it is capable of forming of a subject at a particular distance. An unfocused or out-of-focus image appears blurry, ill-defined and deficient in contrast. An in-focus image looks sharp, precisely defined and as rich in contrast as the lens system and viewing conditions permit.

Focussing Scale
Scope sights with adjustable focussing objectives usually have a focussing scale on or adjacent to the movable focus control. The scale, calibrated in feet,yards or metres, permits setting the focus rapidly for targets at known distances. When target distance is unknown, the scope is focussed visually and the scale ignored. Accuracy of focussing scale calibrations should be verified when a scope is new and occasionally thereafter, as discrepancies are not unusual. This may be done by focussing the scope carefully on targets at known distances. If the focussing scale is at odds with reality, have it adjusted by the appropriate service facility or remark it with small pieces of tape or dots of nail polish for personally useful range settings. An optical instrument that focuses erratically or inconsistently should be repaired or replaced.

Haze
Light scattered by particulate matter in the atmosphere, such as dust or moisture droplets. Haze lends a foggy or cloudy appearance to distant objects or scenes, subduing colours and contrast. Haze effects are more apparent when using high magnification optical instruments than when viewing with lower-power optics or the naked eye, and are more pronounced at long range than short range under a given set of atmospheric conditions.

Individual Focus
Refers to a type of binocular in which the ocular of each half must be focussed independently each time the instrument is refocused. Adjusting the focus of an individual-focus binocular is slower than a centre-focus model, but the former is mechanically simpler and, construction quality being equal, potentially less vulnerable to hard knocks.

Lens Aberration
An optical flaw that adversely affects image quality.

Lens Coating
Anti-reflection layer or layers deposited on surfaces of prisms and lenses by vaporizing metallic compounds in vacuum chambers containing the optical elements to be coated. Lens coating reduces loss of light and image degradation caused by scattering of light reflected by lens surfaces. Traditional lens coatings comprise a single anti-reflection layer applied to each significant glass surface. More modern multiple-layer lens coatings consist of three or more anti-reflection layers per surface. Both single and mufti-layer coatings are effective when they are applied appropriately.

Luminosity
Radiating or reflecting light. Also a measure of the brightness of alight source or of a reflective surface expressed quantitatively according to rigorously defined criteria.

Magnification
Relationship between the apparent size of an object as viewed through an optical instrument and the apparent size of the object as seen with the naked eye. For example, a scope that makes an object look four times larger than it appears when viewed directly has a magnification of four times, usually expressed as 4X. A magnification designated by a number smaller than one indicates that the viewing device makes the subject appear proportionately smaller than when seen with the unaided eye. An instrument of 0.9X magnification reduces the apparent size of the subject to only 90% of what it would seem in direct viewing. Note that the term magnification is used even when the optical device “minifies.” As a practical matter, nearly all sporting optics yield positive magnifications that enlarge the viewing image. The magnification bears a direct relationship to the apparent distance of the viewed object: the greater the magnification, the closer the object appears. Dividing the actual distance of the object by the magnification indicates the apparent distance of the object as viewed through the optical system. An object 100 yds. distant would appear as though it were 50 yds. distant when viewed through a 2X scope and just 10 yds. distant through a IO X scope.

Mirage
Optical phenomenon that occurs when air near the ground is significantly denser than the air above it, creating visible reflected images of distant objects or targets. Less extreme mirage phenomena are of concern to outdoor target shooters, appearing as a shimmer that makes precise aiming difficult or impossible, or that may cause an apparent displacement of the target that leads to erroneous shot placement as the shooter fires at the mirage image rather than the actual target. High-power scope sights make mirage more noticeable, but they also allow the experienced marksman to judge the mirage effect with greater certainty, and compensate for it to the best of his or her ability. The term mirage is also broadly applied to the heat shimmer from a hot gun barrel, which may disrupt the sighting image. Extra-long lens shades offer relief from such heat shimmer.

Objective
The objective lens or lens group forms the image of a distant target or subject at or near the focal point of the optical system. The objective is located at the front of the instrument.

Ocular
The ocular lens or lens group enlarges the image the objective lens forms and allows the viewer’s eye to see it clearly despite its proximity to the eye. The ocular is the part of the optical system nearest the viewer’s eye and is the rearmost lens group of a scope sight. The ocular lenses of nearly all rifle and handgun scopes may be focussed to suit the user’s vision, thus providing the sharpest possible view of the reticle and of the image formed by the scope’s objective lens.

Parallax
Apparent shift in position of a viewed object attributable to the difference between two separate and distinct points of view. In a scope sight, parallax can cause an aiming error, or parallax error, when the target image is not formed in the same plane as the reticle. The condition may be detected by moving the aiming eye progressively away from the centre of the ocular toward the edge of the lens without moving the scope. If the target and reticle shift position slightly relative to each other, parallax error exists and will cause a corresponding shift in the centre of impact. The more the eye moves away from the scope’s optical axis, the greater the parallax error. Parallax error does not occur when the aiming eye is well centred with respect to the ocular lens, even though the conditions for a potential error are present. With a fixed-focus scope sight that has been factory-set for optimum focus at a specific distance, the potential for parallax error exists whenever targets are nearer or farther than the range for which the optics were regulated. In most cases the amount of error will not be significant in the context of normal field shooting. Parallax error can be avoided satisfactorily by keeping the aiming eye reasonably well centred. High-power varmint and target scope sights have adjustable objectives that permit focussing the scope over a wide range of target distances. Focussing such scopes carefully assures maximum image sharpness and also eliminates potential parallax error at the distance for which the scope is focussed. With the scope focussed properly, moving the eye off centre will not cause a shift in the relative positions of reticle and target, and the centre of impact will not be affected by the shift in eye position relative to the optical axis.

Objective lens
Used in pairs in a binocular barrel between the objective and ocular lenses, right-angle porno prisms erect the inverted image formed by the objective lens group. They also “fold” the light path, permitting the binocular barrel to be made shorter than if a non-prismatic optical design were used. The offset required between the porno prisms in each pair gives the binocular barrels a corresponding offset between the objective and ocular sections.

Relative Brightness
Relative brightness numbers are an attempt to quantify the “brightness” of scope sights and binoculars to facilitate comparison. The relative brightness number is the square of the diameter of the instrument’s exit pupil, expressed in millimetres. You can determine the size of the exit pupil, if it isn’t stated in product literature, by dividing the useful aperture of the objective lens, in millimetres, by the magnification, or power, of the instrument. For example, a 4X rifle scope with a 40 mm objective would have a 10 mm exit pupil (40 = 4 = 10) and a relative brightness of 100 (l Oz). The relative brightness reflects the optical truth that, all other factors being equal, large-diameter objectives admit more light than small-diameter objectives. More light can pass through a large window than through a small one.

Resolving Power (Resolution)
The ability of a lens or lens system to form an image in which fine subject details are clearly differentiated. The higher the resolving power, or resolution, the more precisely the subject detail is rendered.

Reticle
In a rifle or handgun scope, the reticle is an aiming reference consisting of crosswires, dot, pointed post or other distinct shape that appears superimposed on the field of view. The reticle is positioned within the optical system to coincide with the plane of focus of the objective lens or lens group. Some scope sights are offered with a choice of reticle styles to accommodate subjective preferences and/ or match function to application. As a rule, to which there are exceptions, hunting-style scope sights have relatively bold reticles that aid rapid aiming, while target and varmint models feature finer reticles that subtend less of the target and may be less prominent, but are conducive to precise shot placement when aiming carefully and deliberately. Some spotting scopes and binoculars incorporate a scaled reticle intended to aid in estimating target distance or size.

Roof prism
Also called Dach prisms (Dach is the German word for roof), these relatively complex prisms erect the image in binoculars and “fold” the light path to allow shortening the barrels. Roof prisms are more difficult, and therefore more expensive, to manufacture than porno prisms, but they allow designing the binocular with compact, straight barrels, reducing size and often reducing weight. For a given level of quality, a pair of binoculars incorporating roof prisms is likely to cost more than one of similar power and light transmission that uses porno prisms. When minimizing instrument size and weight is not a major criterion for selection, overall optical and mechanical quality are more important than prism configuration.

Spherical Aberration
Causes varying degrees of image distortion. Light rays entering the outer portions of the lens are brought to a focus closer to the lens than light rays passing through the center of the lens. The resulting distortion is more likely to be noticed in photographs than when viewing through such a lens.

Twilight Factor
Most often associated with binoculars, the twilight factor is a numerical expression of the telescopic effect in dim light. It may also be calculated for scope sights. The twilight factor is derived by multiplying the magnification, or power, by the useful objective diameter, in millimetres, and then extracting the square root. In the case of a 4X scope sight with a 40 mm objective, the calculation would be 4 x 40 = V ’160 = 12.64911. The twilight factor assumes realistically that in dim light, all other factors being equal, viewing instruments with higher magnifications and larger objectives will outperform those instruments with lower power and lesser light gathering capability.

Variable Power
Variable-power scope sights, spotting scopes and binoculars have a control that allows the user to adjust the magnification over a predetermined range, as with a photographic “zoom” lens.

Wide-Field
Wide-field viewing or sighting optics provide a broader field of view at any given distance than would a conventional non-wide-field instrument of the same magnification.

Sighting And Glasses
Shooting with protective glasses presents a different sight picture than without glasses because of the intervening layer of plastic or glass. Many shooters have noted that there is a displacement of objects in the field of view and believe the use of protective lenses introduces a sighting error.
Instead, as the diagram indicates, the direction of the gun is determined by the alignment of the sights with the target. The eye only sees the alignment after it has taken place. Even if there were a mirror or prism behind the sights, so that the sight picture could be viewed from entirely around a corner, it would make no difference. By the same reasoning, this principle also applies to optical sights as well as iron sights.

Alarm: a signal given by an EDS that indicates to the operator that a detection of explosive material has been made. For a technological system such as an IMS the alarm might be either audio (e.g., a buzzer sounds) or visual (e.g., a message on a computer screen). In the case of a canine, the alarm is some form of behaviour by the dog which the handler interprets as a detection.

Alarm resolution: the process by which an operator determines whether an alarm is the result of a threat item being present, or whether in fact there is no threat item present.

Alarm threshold setting: the signal level above which an EDS is set to alarm. An EDS may make a detection of an amount of explosive below the alarm threshold setting, but it will then be assumed that the signal obtained is either (1) a nuisance alarm or (2) noise.

Ammonia dynamites: a class of dynamites in which a portion of the nitroglycerin is replaced by ammonium nitrate and nitroglycol. These dynamites are lower in cost and less sensitive to shock and friction than straight dynamites.

Ammonia-gelatin dynamites: gelatin dynamites where part of the nitroglycerin/nitrocellulose gel is replaced by less costly ammonium nitrate.

Ammonium nitrate: an explosive compound, NH4NO3. It is the main ingredient of ANFO, and of some water-gel explosives.

Analyte: in analytical chemistry, the compound that is being studied, analysed, or identified.

ANFO: a mixture of ammonium nitrate and fuel oil, often used in vehicle bombs.

Astrolite: a commercially available two-part explosive. One component is a liquid and the other is a solid.

Attenuation coefficient: a measure of how much an incident probe (e.g., electromagnetic radiation) is attenuated as it passes through a given substance.

Atomic explosion: an explosion caused by the breaking up (fission) or joining together (fusion) of atomic nuclei. This is the type of explosion occurring when a nuclear weapon is detonated.

Atomic number: the total number of protons in the nucleus of an atom, equal to the nuclear charge. Represented by the symbol Z.

Backscatter x-ray system: any x-ray system that detects objects (including explosives) based on the images produced from reflected x-rays.

Binary explosive: an explosive material containing two different explosive compounds.

Black powder: a low explosive which is a mixture of potassium nitrate (KNO3), charcoal, and sulfur. It is frequently used in mail bombs and pipe bombs.

Blasting agent: a chemical composition or mixture, consisting mainly of ammonium nitrate, which will detonate when initiated by high explosive primers or boosters. Blasting agents contain no nitroglycerin and are relatively insensitive to shock and friction.

Blasting cap: a device containing a small amount of primary high explosive, used for detonating a main charge of secondary high explosive.

Blasting slurries: a blasting agent consisting of NCN mixtures in a gel-like consistency.

Blast pressure wave: the wave of hot, very high-pressure gases travelling outward from an explosive detonation. The effect of this wave decreases as distance from the point of explosion increases.

Bomb: any device containing explosive or incendiary material that is designed to explode or ignite upon receiving the proper external stimulus.

Bombing: an illegal detonation or ignition of an explosive or incendiary device.

Bomb detection: the discovery and identification of bombs that are being smuggled, or used for some illicit purpose. Bomb detection differs from explosives detection in that the detection may or may not be based on the detection of the explosive material in the bomb. The detection may be based on the detection of some other bomb component, such as metal parts that are identified using metal detection.

Bonding agent: a material that is added to a chemical mixture in order to help bind the
components together.

Boosters: secondary explosives placed between the primary high explosive (blasting cap) and the main explosive charge, with the purpose of amplifying the detonation wave from the primary high explosive.

Brisance: the destructive fragmentation effect of a charge on its immediate vicinity.

Bulk explosives detection system: any EDS which directly detects a macroscopic solid mass of explosive material. This is often (but not always) accomplished using x-ray technology, with the explosive material being observed as an object on the x-ray image. Bulk detection is in contrast to trace detection, where the explosive material is detected from vapour or particulate residue. In contrast to a trace detection system, a bulk detection system will never detect explosives if only residue is present.

C-3: a military plastic explosive, composed of approximately 80 percent RDX and 20 percent plasticizer. Also known as composition C-3, it was the predecessor to C-4.

C-4: a military plastic explosive composed primarily (approximately 90 percent) of RDX. Also known as composition C-4.

Canine detection: the detection of explosives, narcotics, or other types of chemical compounds through the use of a dog that is trained to sniff out these substances.

Carrier gas: In IMS technology, the carrier gas (also called dopant) is a gas which is added to the inlet air flow containing the sample. The purpose of the carrier gas is to enhance the ionization process, and in some cases to make the sample molecules easier to detect via the formation of a chemical adduct (i.e., a species consisting of the sample molecule attached to a carrier gas molecule or fragment).

Cavity charge: a shaped charge.

Certification: a process through which an EDS is tested and, if it performs successfully, is judged to be suitable for certain applications.

Cf: Californium, a radioactive element that emits neutrons and can be used as a neutron source.

Chemical explosion: an explosion caused by the extremely rapid conversion of a solid or liquid explosive into gases having a much greater volume than the original material.

Chemiluminescence: a trace detection technique in which explosives are detected via light that is emitted from NO molecules in a chemically excited state. The excited state NO molecules are formed through deliberately induced decomposition of the nitro (NO2) groups in the original explosive compound.

Combustible: a material capable of igniting or burning.

Commercial explosives detection system: any EDS that can be purchased on the open market.

Composition B: a plastic explosive that contains approximately equal amounts of TNT and RDX.

Computer tomography, computed tomography: an x-ray technique in which transmission images (“slices”) taken at many different angles through an object are put together to produce a three-dimensional image of the object.

Contraband: any item or material that is smuggled into an area or facility where it is prohibited. For example, in a prison contraband might include weapons, explosives, and narcotics.

Conical-shaped charge: a cone-shaped explosive charge, employed to cut or punch a hole through a target.

Cordeau Detonant: a brand name for detonating cord.

CT: computer tomography.

Deflagration: a subsonic process by which explosives release their energy through a rapid burning or autocombustion process, this process being sustained by the energy release from the material. Low explosives explode via deflagration, and under some circumstances high explosives do also. The terms explosion and deflagration are sometimes used synonymously, with both being in contrast to detonation.

Density: the mass of a substance per unit volume, usually expressed in units of grams per cubic centimetre (gr/cm3).

Detacord: a brand name for detonating cord.

Datasheet: a plastic explosive with a sheet-like structure, containing PETN as the explosive ingredient.

Detonating cord: a cord-like synthetic explosive product, containing PETN as the explosive ingredient.

Detonating Fuse: a brand name for detonating cord.

Detonation: the supersonic process by which a high explosive decomposes and liberates its energy from shock wave compression.

Detonation velocity: the speed at which the shock wave travels through an explosive material.

Detonator: a device, such as a fuse or blasting cap, used to set off explosives.

Dielectric constant: the ratio of electric flux density produced by an electric field in a given material, compared to the density produced by the same field in vacuum. Also called permittivity.

Ditching dynamite: a form of straight dynamite widely used in commercial blasting operations. It is characterized by a high detonation velocity of over 5,185 m/s (17,000 ft/s).

DNT: 2,4-dinitrotoluene, a high explosive compound with a rather high vapour pressure (near one part per million). Molecular formula C7H6N2O4; molecular weight = 182.

Dopant: carrier gas.

Double-beam backscatter x-ray system: a backscatter x-ray system in which there are two x-ray sources and two detectors, so that both sides of an investigated article can be looked at simultaneously.

Dual-axis x-ray system: an x-ray system in which the object under investigation is examined with two x-ray beams coming in at two different angles.

Dual-energy x-ray system: an x-ray system in which the object under investigation is simultaneously irradiated with x-ray beams of two different energies. This allows a wider range of target materials to be detected than if only one beam of one energy were used.

Dynamite: a solid synthetic explosive material, widely used in blasting operations. Dynamite usually contains nitroglycerin as a major explosive component.

ECD: electron capture detector.

Eddy current: a current that is induced around a closed conducting loop by the application of an external magnetic field. Eddy currents currently form the basis of most portal metal detectors.

EDS: explosives detection system.

Effective atomic number: for a substance made up of more than one element, the apparent atomic number that results if the substance is treated as if it were composed only of a single element. It is closely related to the weighted average of the atomic numbers of the constituent elements.

EGDN: ethylene glycol dinitrate. This is a high vapour pressure high explosive that is one of the main explosive ingredients in certain types of dynamite. Its molecular formula is C2H4N2O6; molecular weight = 152.

Electric blasting cap: a blasting cap that is initiated by passing electric current through a bridge wire, thus igniting the primary explosive present in the cap.

Electroluminescent image panel: a panel that is capable of converting electric energy into light.

Electron capture detector: a type of explosives detector wherein gas phase explosives molecules capture electrons from an electron-emitting source to form negative ions. The presence of an explosive is then deduced by observing a decrease in the electron current delivered from the emitting source to a detector.

Electronegativity: the tendency of a molecule to attach an electron.

Explosive bombing: the illegal explosion of a device containing high or low explosive material.

Explosive mixture: a low explosive material composed of a mixture of a combustible and an
oxidizer.

Explosives: Explosives are compounds or mixtures of compounds which when subjected to the appropriate stimulus (heat, shock, friction, etc.) undergo extremely rapid chemical changes that result in the evolution of large volumes of highly heated gases and exert pressure upon the surrounding medium. Explosives can be thought of as energy packets that can release their energy in the microsecond time frame.

Explosives detection system: any device, person, or animal which serves the purpose of detecting explosives. Examples include an ion mobility spectrometer, an x-ray scanner for screening luggage, a trained canine with a handler, and a security guard conducting manual inspection of backpacks and briefcases.

Explosive train: a series of explosions specifically arranged to produce a desired outcome.

EXPRAY: a commercially available, aerosol-based field test kit, able to detect most explosives. Detection is based on colour changes of a special paper when it is treated with one of three types of aerosol spray.

False alarm: any alarm of an EDS which occurs when no explosive material or explosive residue is really present. Such alarms may be caused by chemically similar innocuous compounds, or by system malfunction.

False negative: an indication from an EDS that a person or item being screened for explosives is free of explosive material, when in fact the person or item does have/contain explosives.

False positive: an indication from an EDS that a person or item being screened for explosives has/contains explosive material, when in fact the person or item does not have/contain explosive material.

Flex-X: a military name for Detasheet.

Fluorophore: material capable of fluorescence.

Fluoroscopic imaging: use of a fluorescent screen to view the contents of an opaque object, with the contents appearing as shadows formed by transmission of x-rays through the object.

Forensics: In the sense used herein, the science of trace explosives analysis as related to criminal investigations or other law enforcement work.

Fragmentation bomb: a bomb such as a pipe bomb where explosive material is placed inside a metal or other solid casing, with the casing breaking into fragments that are hurled about the area at high velocity when the bomb explodes.

Free-running explosives: group of blasting agents consisting of NCN in small pellet or granular form.

Ft/s: feet per second, the standard unit for detonation velocities.

Gamma rays: high-energy electromagnetic radiation emitted by certain atoms when they are properly stimulated, as in the technique of TNA.

Gelatin dynamites: a class of dynamites with an explosive base of water-resistant gel, formed by combining nitrocellulose and nitroglycerin.

Granulation: the grain size of an explosive powder, such as black powder.

Guncotton: nitrocellulose.

Handler: the individual controlling a dog that is trained to sniff out explosives or narcotics.

HE: high explosive.

High explosives: explosives that are capable of detonation. Common examples include TNT, RDX, PETN, NG, and EGDN.

High-explosive train: an explosive train involving high explosives.

High-order detonation: complete detonation of an explosive at its highest possible detonation velocity.

HMX: a high explosive, chemically related to RDX. HMX (Her Majesty’s Explosive) is an eight membered ring of alternating carbon and nitrogen atoms, with nitro (NO2) groups attached to the nitrogens. Molecular formula C4H8N8O8, molecular weight = 296. HMX has an extremely low vapour pressure and hence is very difficult to detect using any vapour sniffing technique.

Hydrazine: liquid component of the two-part explosive Astrolite. Hydrazine is also used in rocket fuel.

Hygroscopic: readily absorbing moisture, as from the atmosphere.

Immunochemical: relating to antibody-based techniques applied to trace chemical detection.

Improvised device: a homemade device filled with explosive or incendiary material and containing the components necessary to initiate the device.

Incendiary device: a device constructed with flammable materials designed to produce a burning effect.

Incendiary thermal effect: the burning effect of an explosion. It is relatively insignificant compared to the blast pressure effect.

Infrared radiation: electromagnetic radiation that is less energetic than visible light and more energetic than microwaves.

Instantaneous combustion: a colloquial term for detonation. Detonation is in reality not truly instantaneous, but occurs in a matter of microseconds.

Interference, interferent: any chemical compound that serves to mask the presence of an explosive from a given explosives detection system.

Ion mobility spectrometer (IMS): a trace chemical detector which detects explosives and other chemical compounds using the technique of ion mobility spectrometry.

Ion mobility spectrometry: a technique for the trace detection of explosives and other chemical compounds. In this technique, compounds are first ionized, then identified based on the time that it takes them to travel through a region with an applied electric field.

Jet: the extremely hot, swiftly moving bundle of gases and concentrated power resulting from a directionally directed explosion.

Jet-Axe: a commercially available linear-shaped charge, used to cut through doors, roofs, and walls to obtain access into a building.

Kine-Pak: a commercially available two-part explosive, having excellent shock resistance even after mixture of the two components.

KV: kilovolts, a unit of energy.

KVp: kilovolts potential, x-ray source voltage descriptor.

Lead azide: a primary high-explosive compound, Pb(N3)2.

Lead styphnate: a primary high explosive, often used in blasting caps, C6H3N3O9Pb.

Linear-shaped charge: a type of shaped charge used to cut or slice a target.

Low explosives: explosives which do not detonate, but rather explode via the process of deflagration.

Low-explosive train: an explosive train employing only low explosives.

Low-order detonation: incomplete detonation of an explosive, or detonation at less than maximum detonation velocity.

Magnetic moment: a property of the nucleus of atoms that have a non-zero nuclear spin. These atoms are affected by the application of an external magnetic field, and can give rise to an NMR spectrum.

Mail bomb: any bomb that is sent through the postal service in a letter or package. It is usually designed to detonate when the letter or package is opened.

Mass spectrometer: an instrument that performs mass spectrometry.

Mass spectrometry: a chemical analysis technique in which the molecules to be studied are first ionized and then separated and identified based on their charge-to-mass ratio. Mass spectrometry is performed under conditions of high vacuum, in contrast to IMS which is performed at atmospheric pressure.

Mechanical explosion: an explosion caused by the buildup of excessive pressure inside a solid container, the pressure buildup resulting from the application of heat and hence vaporization of a material inside the container.

Mercury fulminate: a primary high-explosive compound, Hg(OCN)2.

Metal detection: the detection of metals and other conducting materials, usually based on the detection of eddy currents in an applied magnetic field.

Microgram: one millionth of one gram, usually written as mg.

Microrem: a unit of radiation dosage, equal to one millionth of a rem.

Microsecond: one millionth of 1 second, usually written as ms.

Microwaves: electromagnetic radiation that is less energetic than infrared radiation but more energetic than radio waves.

Military dynamite: an explosive (not a true dynamite) used in military construction and demolition work. It is composed of 75 percent RDX, 15 percent TNT, 5 percent motor oil, and 5 percent cornstarch.

Military explosives: explosives manufactured primarily for military applications. Examples include TNT, tetrytol, and C-4.

Milking: a dangerous process by which nitroglycerin is extracted from dynamite.

Milligram: one-thousandth of one gram, usually written as mg.

Millimetre waves: electromagnetic radiation (microwaves) having a wavelength on the order of a few millimetres.

Mine detection: the detection of land or sea mines that are buried or submerged. The detection may be made using metal detection, explosives detection, or some other detection technique.

Nanogram: one-billionth of one gram, usually written as ng.

NCN: nitro-carbo-nitrates.

Negative-pressure phase: the time period following an explosion and after the passing of the outward-going blast pressure wave, during which the pressure at a given point is below atmospheric pressure and air is sucked back into the area. Also called the suction phase. It is less powerful than the positive-pressure phase, but of longer duration.

Nerve agents: chemical agents that harm humans by attacking the nervous system.

Neutron: an elementary particle; along with protons and electrons, one of the three particles that make up atoms. Used as a probe to look for explosives in the technique of thermal neutron activation. Neutrons are neutral (i.e., they have no electrostatic charge).

NG: nitroglycerin.

Nitro-carbo-nitrates: a type of blasting agent, composed primarily of ammonium nitrate and oil.

Nitrocellulose: a cotton-like polymer treated with sulfuric and nitric acids, and used in the
manufacture of certain explosives.

Nitroglycerin, nitroglycerine: a high vapour pressure (vapour pressure approximately one part per million) high-explosive compound that is the explosive ingredient in certain types of dynamite. Molecular formula C3H5N3O9; molecular weight = 227.

NMR: nuclear magnetic resonance.

Non-electric blasting cap: a blasting cap in which the primary explosive material is set off using a flame.

Nuclear detection system: any bulk explosives detection system based on the properties of the nuclei of the individual atoms within the explosives material, including TNA, NMR, and QR systems.

Nuclear magnetic resonance: a bulk explosives detection technique based on the magnetic
properties of the hydrogen atoms within the explosive being detected.

Nuisance alarm: In trace detection, an alarm caused by the detection of explosive material, but where the detection results not from a bomb or other contraband explosives but rather from a non threat item. For example, in a portal that screens personnel for explosives, detection of NG on a heart patient using NG tablets would be a nuisance alarm. A nuisance alarm is different from a false alarm, since in the case of a false alarm no explosive material is actually present.

Oxidizer: any substance that chemically reacts with another substance to increase its oxygen content.

Particulate: contamination in the form of residual particles attached to clothing, furniture, luggage, skin, or some other surface.

Parts per billion: a quantitative measure of pressure and certain other quantities. When used in reference to explosives vapour pressures, one part per billion means that under equilibrium conditions the air above the explosive material will contain one molecule of explosive vapour for every billion molecules in the air itself.

Parts per million: a measure of explosive vapour concentration analogous to parts per billion, but a thousand times more concentrated. Thus one part per million of explosives vapour in air means one molecule of explosive vapour per every million molecules in the air itself.

Parts per trillion: a measure of explosives vapour concentration analogous to parts per billion, but a factor of one thousand less concentrated. Thus one part per trillion of explosives vapour in air means one molecule of explosive vapour per every trillion molecules in the air itself.

Pentolite: a commonly employed booster explosive, composed of 50 percent TNT and 50 percent PETN.

Percussion primer: a primer that converts mechanical energy into a flame, such as the primer that is set off by the firing pin in a gun.

PETN: pentaerythritol tetranitrate, a common high explosive. It is used in plastic explosives such as Detasheet and Semtex, and has a low vapour pressure (a few parts per trillion at room temperature and atmospheric pressure). Molecular formula C5H8N4O12; molecular weight =

PFNA: pulsed fast neutron analysis.

Phosphor: any substance that can be stimulated to emit light by incident radiation.

Picogram: one-trillionth of 1 gram, usually written as pg.

PINS: portable isotopic neutron spectroscopy.

Pipe bomb: a homemade bomb in which explosive material is packed into a section of (usually metal) pipe. Upon explosion, the pipe may shatter, and the propelled fragments thus produced can do much damage to people and property.

Pixel: the smallest resolvable spot on a computer or television screen.

Plastic explosives: high-explosive materials that have the general consistency of plastic. They are usually composed of RDX and/or PETN, along with a small amount of oil or elasticizing agent. Examples include C-4, Detasheet, and Semtex.

Portable isotopic neutron spectroscopy: a portable explosives detection system based on the emission of gamma rays when a material is bombarded with neutrons from a Cf source.

Portal: a walk-through, booth-like structure which serves the purpose of screening personnel for contraband. Examples include the metal detection portals currently deployed in airports, and various types of explosives detection portals that are now on the market or in development.

Positive-pressure phase: the brief time after a detonation in which the local pressure is much greater than atmospheric pressure, due to the outward-moving blast pressure wave.

Post-blast analysis: analysis of the site of an explosion to attempt to identify the type of explosive that was used.

Potassium chlorate: an explosive compound, KClO3.

Potassium nitrate: a crystalline compound, KNO3, used in the manufacture of explosives, pyrotechnics, and propellants.

Preconcentrator: any mechanical device designed to collect a dilute trace chemical sample and concentrate it, prior to delivery into a detector.

Prill: the loose, powder form of an explosive (as opposed to gel form) or a compressed pellet thereof. The ready made ANFO explosive is also marketed under the name “Prills.”

Primacord: a brand name for detonating cord.

Primary explosives: high-explosive compounds or mixtures that, when present in small quantities, can convert the process of deflagration into detonation. Primary explosives are used to induce detonation of a secondary explosive.

Primer: a cap or tube containing a small amount of primary explosive and used to detonate a secondary main charge.

Primex: a brand name for detonating cord.

Probability of detection – P(d): the probability that a certain EDS can detect a certain amount of a given type of explosive under a particular set of conditions. If a positive detection is always made under these conditions, the probability of detection would be 100 percent. If a detection is made only half the time, the probability of detection would be 50 percent. In general, a large number of experimental trials need to be conducted to accurately determine this parameter.

Propellants: explosive compounds or mixtures used for propelling projectiles or rockets.

Pulsed Fast Neutron Analysis: a nuclear screening technique which measures the elemental composition of the object being scanned through neutron interaction with elemental constituents of the object, resulting in characteristic gamma rays.

Pyrodex: a low-explosive material used as a filler in some improvised devices. Developed by Hodgdon Powder Company, this propellant is available in powder or pellet form. Pyrodex has 30 percent more power than common black powder.

Pyrotechnics: physical mixtures of fuel and oxidizer powders, used to produce light (e.g., fireworks), sound, heat, or smoke.

Q: quality factor, electronics-related term defining the selectivity of a resonant circuit.

QR: quadrupole resonance.

Quadrupole resonance: a bulk explosives detection technique in which the material under investigation is probed using rf radiation. This results in excitation of the nuclei of nitrogen atoms, which emit photons of a characteristic frequency when they relax. The resulting signal is specific for a certain type of nitrogen-containing compound.

Random screening: performing explosives detection on a randomly chosen fraction of a large number of people or items. For example, a security checkpoint might wish to screen every fourth person entering a secure facility. Random screening has the advantage of providing a deterrent against the illicit transport of explosives into a given area, while at the same time being less time consuming than uniform screening. RDX: a high explosive, cyclotrimethylenetrinitramine, also known as cyclonite. The abbreviation RDX stands for “research and development explosive.” RDX is the main ingredient of C-4, and is also used in Semtex. It has a low vapour pressure (low parts per trillion at room temperature and atmospheric pressure). It consists of a six-membered ring of alternating carbon and nitrogen atoms, with nitro (NO2) groups attached to the nitrogen atoms. Molecular formula C3H6N6O6; molecular weight = 222.

RF: radio frequency.

Safety fuse: a flame-producing source used in some non-electric blasting caps.

Saltpeter: potassium nitrate.

Secondary explosives: high-explosive compounds or mixtures that are generally initiated to detonation by intense shock. Secondary explosives are generally less sensitive than primary explosives, but pack more explosive power.

Secondary high-explosive boosters: explosives which provide the detonation link in an explosive train between the very sensitive primary high explosives and the comparatively insensitive main charge high explosives.

Secure area, secure facility: any area or facility where access is restricted by appropriate entry controls. Entry normally involves some form of identity verification for the entering individual. It may also include contraband screening.

Security checkpoint: any checkpoint at an entrance to a secure area that administers some sort of entry control. It may also involve screening for contraband, including explosives.

Semtex: a type of plastic explosive, normally containing both RDX and PETN.

Shaped charge: specially shaped explosive charges that are used to cut or punch holes in solid materials such as steel and concrete.

Shock wave: a sharp discontinuous pressure disturbance travelling faster than the speed of sound. A shock wave is created when a high explosive detonates.

Shrapnel: precut or preformed objects (e.g., metal fragments, nails) placed in or attached to a bomb. When the bomb explodes, these objects are hurled at high velocity, with much potential damage to people and property.

Single-energy transmission x-ray scanner: an x-ray scanner using only a single x-ray beam, in which the portion of the beam that penetrates the object under investigation is detected and used to produce the x-ray image.

Smokeless powder: an explosive material (double-base propellant) in powder form, often containing nitroglycerin (typically 40 percent by weight) as the explosive ingredient.

Sodium chlorate: an explosive compound, NaClO3.

Sodium nitrate: a chemical compound, NaNO3. It is sometimes added to dynamite to increase the oxygen content and hence improve combustion.

Specificity: the ability of a chemical analysis technique to distinguish similar chemicals from one another. The greater the specificity, the more certain the identification of a particular compound can be.

Straight dynamites: a class of dynamites containing nitroglycerin as the explosive base.

Tandem mass spectrometry: a technique of chemical analysis, also referred to as mass spec/mass spec, or simply MS/MS. Essentially, it involves sending analyte molecules through two mass spectrometers consecutively, in order to increase the specificity of the system.

Tetramino nitrate: a highly sensitive primary high explosive, which can be formed from the reaction of ammonium nitrate with brass or bronze tools.

Tetryl: a high-explosive compound, similar in structure to TNT. Molecular formula C7H5N5O8; molecular weight = 287.

Tetrytol: a military explosive composed of approximately 75 percent tetryl and 25 percent TNT.

Thermal neutron: a neutron having an energy that is typical of neutrons at room temperature.

Thermal neutron activation: a bulk explosives detection technique, in which explosives are detected by the emission of characteristic radiation (gamma rays) that occurs when the explosive material is irradiated with thermal energy neutrons.

Threat: the event or occurrence which a protective measure is intended to guard against.

Threat consequence: the results of a particular threat event occurring, including death or injury to personnel, and damage to property.

Threat item: the item that an EDS is designed to detect, i.e., a bomb or contraband explosives material.

Threat probability: the likelihood of a particular threat event actually occurring, on a scale of 0 percent (no probability of occurring) to 100 percent (certainty that the event will occur).

Throughput rate: the rate at which an EDS can process the people or objects being screened. It is generally expressed in units such as people per hour for a personnel portal, or bags per hour for an x-ray baggage scanner.

TNA: thermal neutron activation.

TNT: 2,4,6-trinitrotoluene, a common high explosive with a moderate vapour pressure (near one part per billion at room temperature and atmospheric pressure). Molecular formula C7H5N3O6; molecular weight = 227.

Tovex: a trade name for certain water-gel based explosives.

Trace explosives detection system: any EDS that detects explosive materials by collecting and identifying trace residue from the material. This residue may be in the form of either vapour or particulate. Trace detection is in contrast to bulk detection.

Two-part explosives: explosives that consist of two separate components, which are sold together in separate containers and need to be mixed together prior to detonation.

Ultraviolet light: electromagnetic radiation that is less energetic than x-rays but more energetic than visible light.

Uniform screening: Performing explosives detection on all persons or items passing through a given security checkpoint, applying the same screening process to all of them. Uniform screening is in contrast to random screening.

Vapour generator: any device designed to produce calibrated amounts of vapour of a particular compound.

Vapour pressure: the quantity of vapour (usually expressed in terms of a concentration) of an explosive compound that exists above the compound in air at equilibrium under a specified set of conditions.

Water-gel explosives: explosive mixtures (slurries) consisting of saturated aqueous solutions of ammonium nitrates and other nitrates.

Wavelength: a property of electromagnetic radiation that is inversely proportional to its energy.

Working lifetime: the time period during which a given EDS is useful. For both a canine and an IMS, a typical working lifetime might be on the order of 10 years.

X-ray absorption coefficient: the fraction of incident x-rays that is absorbed by a given material.

X-ray backscatter coefficient: the fraction of incident x-rays that is backscattered (i.e.,
reflected) by a given material.

X-rays: high-energy electromagnetic radiation with wavelength in the approximate range of 0.05 angstroms to 100 angstroms (one angstrom = 1 A = 100 billionths of one centimetre). Less energetic than gamma rays.

X-ray transmission coefficient: the fraction of incident x-rays that pass through a given material.

Z: symbol for atomic number.

Back Stop 
Sometimes called Butts or Butt stop, generally a raised area that prevents bullets or projectiles leaving the range.

Backing Cards 
Card behind scoring targets to either increased vision of the bullet hole or confirm amount of shots in one hole.

Bench Rest 
Heavy table equipped with a Rifle Rest and Sand Bags for Bench Rest competition or sighting in firearm to zero.

Bullet Blocks 
Wooden blocks used to stand ammunition in.

Bullet Catcher or Collector Systems
Situated at the stop butts that prevent ricocheting bullets or projectiles from leaving the range area.

Butts  
Area behind a raised mound with an underground trench to allow.

Butt Markers
People who score and change the targets for shooting competitors.

Cards 
Targets

Cease Fire!
Range Officers Order to Stop shooting.

Ear Protection 
Ear Muffs or plugs, both have as high safety rating,. (red box or packet) Many shooters using low velocity rimfire rifles consider that they are un-necessary but the sound of a .22 is well above the damage area and hearing loss will result over long exposure. It is a good idea to use them as it increases concentration by blocking out un required noise.

Fire!
Range Officers Order to commence shooting.

Firing Line
A Line of Competitors in a Shooting Competition.

Firing Point 
Area where firearms are discharged at the targets.

Full Bore or Big Bore 
NRA clubs that originally shot the military cartridge of the day, now shooting .308 Winchester(7.62×51  and .223 Remington. (5.56 Nato). Clubs originally formed in the 1870s began shooting with what was then considered Small bore rifle the Martini Henry rifle in .450/577 as it was small in comparison to the .69 calibre rifle and larger that preceded it.

Load! 
Range Officers Order to load the loaded magazine into the rifle or load a single round of ammunition into the chamber of the firearm.

Mound 
A mound of earth sometimes used as a firing line or firing point, but often used to describe earth butt stop or back stop for bullets and projectiles.

Range Users Register  
Register that all visitors and Members must fill in when in attendance at Range.

Red Flag 
Red Flags 1.20 m x .90 m at gates and extremities to inform that Range is in use.

Rifle Rest 
Steel Mechanism for preventing human movement to the firearm for Bench Rest Competition or sighting in the firearm to zero.

Rifle Racks 
Rack of timber padded with felt to stand firearms in safely, muzzles pointing upwards, protecting them from slipping and falling.

Sand Bags 
Used to support rifle in fixed position on bench rest. For Bench Rest Competition or sighting in the firearm to point of zero.

Shooting Jackets 
Jacket with padding in specific areas and ability to restrict movement of the upper body.

Small Bore
Clubs that shoot firearms of .22 calibre or less, mainly rimfire.

Spotting Scope 
Optical telescope on stand used for spotting bullet holes in paper or sighting in a firearm.

Timer 
Stop watch or other electronic device that gives audible warning for sequences of shots.

Training Room
Educational area.

Wind Flags 
Small flags at the sides of the range to give guidance on wind conditions.