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.
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