The case, which had been elastically expanded by high pressure, contracts slightly, which eases its removal from the chamber when pulled by the extractor. After the bullet exits the barrel, the gases are released to the surroundings as ejectae, and the chamber pressure drops back down to atmospheric level. bullet) 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. When the pressure builds up sufficiently to overcome the fastening friction between the projectile (e.g. 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. 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 (but not detonate). 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. 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. To perform a firing, the round is first inserted into a "ready" position within the chamber aligned with the bore axis (i.e. In modern self-loading firearms, the round also enables the action mechanism to use part of the propellant energy (carried by the cartridge itself) and cyclically load new rounds of ammunition to allow quick repeated firing. The primary purpose of a cartridge is to offer a handy pre-assembled "all-in-one" package that is convenient to handle and transport, easily inserted into the breech (rear end) of the barrel, as well as preventing potential propellant loss, contamination or degradation from moisture and the elements. 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 close combat (particularly cavalry charges) as well as complicating the logistics of ammunition. 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 (from a slow match, a small charge of gunpowder in a flash pan, or a percussion cap) to set off the shot. The cartridge was invented specifically for breechloading firearms. In other cases, the artillery shell is separate from the propellant charge.Ī 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. Some artillery ammunition uses the same cartridge concept as found in small arms. Military and commercial producers continue to pursue the goal of caseless ammunition. Only the centerfire and rimfire survived mainstream usage today. Although in popular usage the term "bullet" is often informally used to refer to a complete cartridge, it is correctly used only to refer to the projectile.Ĭartridges 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 ( rimfire) inside the walls on the fold of the case base that is shaped like a cup (cupfire, now obsolete) in a sideways projection that is shaped like a 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). rim, which provides the extractor on the firearm a place to grip the casing to remove it from the chamber once fired Ī cartridge or a round is a type of pre-assembled firearm ammunition packaging a projectile ( bullet, shot, or slug), a propellant substance (usually either smokeless powder or black powder) and an ignition device ( primer) within a metallic, paper, or plastic case that is precisely made to fit within the barrel chamber of a breechloading gun, for the practical purpose of convenient transportation and handling during shooting. propellant, for example gunpowder or cordite Ĥ. cartridge case, which holds all parts together ģ. A modern round consists of the following:Ģ.
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