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Ammunition is Effected by Temperature

Free Stuff September 14, 2008

Ammunition is Effected by Temperature

Temperature has a marked effect on both velocity and pressure. Factory ammunition is, as a rule, rather conservatively loaded so that no danger will result even under extremes of temperature.
Twenty years ago a large quantity of 6.5 x 55 ammunition was imported into Australia, (I was responsible for a few million round of it) It was 139 grain FMJ brass case with a berdan primer I suspect made by Norma in Sweden. In normal conditions it was excellent ammunition. (I once shot a five shot.500 inch group at 200m with it). There were reports that it had blown up guns, on investigation this was not the same ammunition only the same calibre. It got everybody talking though.

A southern importer had imported blank ammunition in this calibre and had replaced the wooden blank projectiles with 140 grain soft points. This would not have been …

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Exploding Barrel Blockages

Free Stuff September 12, 2008

Exploding Barrel Blockages

Bore Blockages

Obstructions in a firearm barrel are almost certain to damage the barrel on firing.
The kind and amount of damage depend on location of the obstruction, on its mass (weight), and on the type and thickness of the barrel. A very great variety of results are possible. I have known of them killing the shooter next on the firing line, and only giving the owner of the firearm a sore shoulder. This is the extreme but it can and does happen.

An obstruction close in front of the cartridge in the chamber has the effect of increasing the chamber pressure. An obstruction in the middle or forward part of the barrel produces a local injury.
The action of an obstruction does not depend on trapping air. Experiments with coils of wire and other open obstructions resulted in damage about the same as solid obstructions of …

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Glossary For Optics

Free Stuff May 22, 2008

Optical Glossary

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 …

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