Cartridge (firearms)
A cartridge, also known as a round, is a type of pre-assembled firearm ammunition packaging a projectile, a propellant substance and an ignition device within a metallic, paper, or plastic case that is precisely made to fit within the barrel chamber of a breechloading gun, for convenient transportation and handling during shooting. Although in popular usage the term "bullet" is often used to refer to a complete cartridge, the correct usage only refers to the projectile.
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 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.
File:Cartridge Sample 2.jpg|right|thumb|upright=2|A variety of rifle cartridges:.17 HM2.17 HMR.22LR.22 Win Mag R/F.22 WMR.17/23 SMc 5mm/35 SMc.22 Hornet.223 Remington.223 WSSM.243 Win.243 Win Improved .25-06 Remington.270 Winchester.308 Winchester.30-06 Springfield.45-70 Government.50-90 Sharps
Type
Cartridges can be categorized by the type of primer, which is a small charge of an impact-sensitive explosive compound located:- At the center of the [|case head]
- Inside the rim
- Inside the walls on the fold of the case base that is shaped like a cup
- In a sideways projection that is shaped like a pin
- In a lip
- In a small bulge shaped like a nipple at the case base
- By an electric-sensitive chemical mixture
- By a needle-like firing pin that pierces the case and hits a percussion cap
Design
Purpose
The cartridge was invented specifically for breechloading firearms. Prior to its invention, the projectiles and propellant were carried separately and had to be individually loaded via the muzzle into the gun barrel before firing, then have a separate ignitor compound, to serve as a source of activation energy to set off the shot. Such loading procedures often require adding paper/cloth wadding and ramming down repeatedly with a rod to optimize the gas seal, and are thus clumsy and inconvenient, severely restricting the practical rate of fire of the weapon, leaving the shooter vulnerable to the threat of close combat as well as complicating the logistics of ammunition.The primary purpose of using a cartridge is to offer a handy pre-assembled "all-in-one" package that is convenient to handle and transport, easily loaded into the breech of the barrel, as well as preventing potential propellant loss, contamination or degradation from moisture and the elements. In modern self-loading firearms, the cartridge case also enables the action mechanism to use part of the propellant's energy and cyclically load new rounds of ammunition to allow quick repeated firing.
To perform a firing, the round is first inserted into a "ready" position within the chamber aligned with the bore axis. While in the chamber, the cartridge case obturates all other directions except the bore to the front, reinforced by a breechblock or a locked bolt from behind, designating the forward direction as the path of least resistance. When the trigger is pulled, the sear disengages and releases the hammer/striker, causing the firing pin to impact the primer embedded in the base of the cartridge. The shock-sensitive chemical in the primer then creates a jet of sparks that travels into the case and ignites the main propellant charge within, causing the powders to deflagrate. This rapid exothermic combustion yields a mixture of highly energetic gases and generates a very high pressure inside the case, often fire-forming it against the chamber wall. When the pressure builds up sufficiently to overcome the fastening friction between the projectile and the case neck, the projectile will detach from the case and, pushed by the expanding high-pressure gases behind it, move down the bore and out the muzzle at extremely high speed. After the bullet exits the barrel, the gases are released to the surroundings as ejectae in a loud blast, and the chamber pressure drops back down to ambient level. The case, which had been elastically expanded by high pressure, contracts slightly, which eases its removal from the chamber when pulled by the extractor. The spent cartridge, with its projectile and propellant gone but the case still containing a used-up primer, then gets ejected from the gun to clear room for a subsequent new round.
Components
A modern cartridge consists of four main components: the case, the projectile, the propellant, and the primer.Case
The main defining component of the cartridge is the case, which gives the cartridge its shape and serves as the integrating housing for other functional components, it acts as a container for the propellant powders and also serves as a protective shell against the elements; it attaches the projectile either at the front end of the cartridge or inside of the cartridge, and align it with the barrel bore to the front; it holds the primer at the back end, which receives an impact from a firing pin and is responsible for igniting the main propellant charge inside the case.While historically paper had been used in the earliest cartridges, almost all modern cartridges use metallic casing. The modern metallic case can either be "bottleneck", whose frontal portion near the end opening has a noticeably smaller diameter than the main part of the case, with a noticeably angled slope in between, or "straight-walled", where there is no narrowed neck and the whole case looks cylindrical. The case shape is meant to match exactly to the chamber of the gun that fires it, and the "neck", "shoulder", and "body" of a bottleneck cartridge have corresponding counterparts in the chamber known as the "chamber neck", "chamber shoulder", and "chamber body".
Some cartridges, like the.470 Capstick, have what is known as a "ghost shoulder", a very slightly protruding shoulder, and can be viewed as a something between a bottleneck and straight-walled case. A ghost shoulder, rather than a continuous taper on the case wall, helps the cartridge to line up concentrically with the bore axis, contributing to accuracy. The front opening of the case neck, which receives and fastens the bullet via crimping, is known as the . The closed-off rear end of the case body, which holds the primer and technically is the case base, is called the case head, as it is the most prominent and frequently widest part of the case. There is a circumferential flange at the case head called a rim, which provides a lip for the extractor to engage. Depending on whether and how the rim protrudes beyond the maximum case body diameter, the case can be classified as either "rimmed", "semi-rimmed", "rimless", "rebated", or "belted".
The shape of a bottleneck cartridge case also affects the amount of attainable pressure inside the case, which in turn influences the accelerative capacity of the projectile. Wildcat cartridges are often made by reshaping the case of an existing cartridge. Straight-sided cartridges are less prone to rupturing than tapered cartridges, in particular with higher pressure propellant when used in blowback-operated firearms.
In addition to case shape, rifle cartridges can also be grouped according to the case dimensions of a cartridge, this is usually referring to the cartridge's overall length, which in turn dictates the minimal receiver size and operating space needed by the action, into either "mini-action", "short-action", "long-action", or "magnum-action" categories.
- Mini-action cartridges are usually intermediate rifle cartridges with a COL of or shorter in length, which is most commonly exemplified by the.223 Remington;
- Short-action cartridges are usually full-powered rifle cartridges with a COL between, which is most commonly exemplified by the.308 Winchester;
- Long-action cartridges are usually traditional full-powered rifle cartridges with a COL between, which is most commonly exemplified by the.30-06 Springfield;
- Magnum-action cartridges are rifle cartridges that are both longer, wider and more powerful than traditional long-action rifle cartridges, with a COL between, including some of the long-action cartridges with a case head larger than diameter, which is most commonly exemplified by the.375 Holland & Holland Magnum.
Steel casing is used in some plinking ammunition, as well as in some military training ammunition, along with Russia and China. Steel is less expensive to make than brass, but it is far less corrosion-resistant and not feasible to reuse and reload. Military forces typically consider service small arms cartridge cases to be disposable, single-use devices. However, the mass of the cartridges can affect how much ammunition a soldier can carry, so the lighter steel cases do have a logistic 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 is that propellant gas can blow back past the neck and leak into the chamber. Constituents of these gases condense on the chamber wall, and 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 looser chamber tolerances than NATO weapons.
Aluminum-cased cartridges are available commercially. These are generally not reloaded, as aluminum fatigues easily during firing and resizing. Some calibers also have non-standard primer sizes to discourage reloaders from attempting to reuse these cases.
Plastic cases are commonly used in shotgun shells, and some manufacturers offer polymer-cased centerfire pistol and rifle cartridges.