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Ammunition & Firearms Cartridges Primer Powder Built Case

Ammunition & Firearms Cartridges Primer Powder Built Case

Ammunition & Firearms Cartridges

Ammunition & Firearms Cartridges Primer Powder Built Case

Ammunition & Firearms Cartridges Primer Powder Built Case

A cartridge is a type of ammunition packaging a projectile (bullet, shots or slug), a propellant substance (usually either smokeless powder or black powder) and a primer within a metallic, paper or plastic case that is precisely made to fit within the barrel chamber of a breechloading firearm. In popular use, the term “bullet” is often misused to call a complete cartridge, though it technically only refers to the projectile part of the cartridge. Ammunition & Firearms Cartridges Primer Powder Built Case

Cartridges can be categorized by the type of their primers — a small charge of an impact- or electric-sensitive chemical mixture that is located at the center of the case head (centerfire), inside the rim of the case base (rimfire, and the now obsolete cupfire), in a sideways projection that is shaped like pin (pinfire, now obsolete) or a lip (lipfire, now obsolete), or in a small nipple-like bulge at the case base (teat-fire, now obsolete).

Military and commercial producers continue to pursue the goal of caseless ammunition. Some artillery ammunition uses the same cartridge concept as found in small arms. In other cases, the artillery shell is separate from the propellant charge.

A cartridge without a projectile is called a blank. One that is completely inert (contains no active primer and no propellant) is called a dummy. One that failed to ignite and shoot off the projectile is called a dud, and one that ignited but failed to sufficiently push the projectile out of the barrel is called a squib.

Purpose

Primary purpose is to be a handy all-in-one (projectile, right quantity of propellant, primer) for a shot. In modern, automatic weapons, it also provides the energy to move the parts of the gun which make it fire repeatedly. Many weapons were designed to make use of a readily available cartridge, or a new one with new qualities.

The cartridge case seals a firing chamber in all directions excepting the bore. A firing pin strikes the primer and ignites it. The primer compound deflagrates, it does not detonate (that is, it rapidly burns, but does not explode). A jet of burning gas from the primer ignites the propellant.

Gases from the burning powder pressurize and expand the case to seal it against the chamber wall. These propellant gases push on the bullet base. In response to this pressure, the bullet will move in the path of least resistance which is down the bore of the barrel. After the bullet leaves the barrel, the chamber pressure drops to atmospheric pressure. The case, which had been elastically expanded by chamber pressure, contracts slightly. This eases removal of the case from the chamber.

Materials

The projectile (see below) can be made of virtually anything. Lead is a material of choice because of high density, and ductility.

The propellant was long gunpowder, still in use, but superseded by better compositions, generically called Smokeless powder.

The Early primer was simply fine gunpowder poured into a pan or tube where it could be ignited by some external source of ignition such as a fuse or a spark. Modern primers are shock sensitive chemicals enclosed in a small (a few mm) capsule, ignited by percussion. In some instance ignition is electricity-primed, and there may even be no primer at all in such design (the propellant being directly ignited).

The case is commonly made of brass because it is resistant to corrosion. A brass case head can be work-hardened to withstand the high pressures of cartridges, and allow for manipulation via extraction and ejection without tearing the metal. The neck and body portion of a brass case is easily annealed to make the case ductile enough to allow reforming so that it can be reloaded many times.

Steel is used in some plinking ammunition, as well as in some military ammunition (mainly from the former Soviet Union and China). Steel is less expensive than brass, but it is not feasible to reload and reuse steel cases. Military forces typically consider small arms cartridge cases to be disposable, one-time-use devices. However, case weight (mass) affects how much ammunition a soldier can carry, so the lighter steel cases do have a military advantage. Conversely, steel is more susceptible to contamination and damage so all such cases are varnished or otherwise sealed against the elements.

One downside caused by the increased strength of steel in the neck of these cases (compared to the annealed neck of a brass case) is that propellant gas can blow back past the neck and into the chamber. Constituents of these gases condense on the (relatively cold) chamber wall. This solid propellant residue can make extraction of fired cases difficult. This is less of a problem for small arms of the former Warsaw Pact nations, which were designed with much larger chamber tolerances than NATO weapons.

Aluminum cased cartridges are available commercially. These are generally not reloaded as aluminium fatigues easily during firing and resizing. Some calibers also have non-standard primer sizes to discourage reloader from attempting to reuse these cases.

Plastic cases are commonly used in shotgun shells, and some manufacturers offer polymer centerfire cartridges.

Historically paper had been used in the earliest cartridges.

 

Eric Beer | BC Firearm Academy

3229 Fraser St, Vancouver, BC V5V 4B8

604-592-2410

http://bcfirearmsacademy.ca

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