Editing Cartridge (firearms) (section)

===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 [[muzzleloading|via the muzzle]] into the [[gun barrel]] before firing, then have a separate [[fire making|ignitor]] compound (from a burning [[slow match]], to a small charge of [[gunpowder]] in a [[flash pan]], to a metallic [[percussion cap]] mounted on top of a "nipple" or cone), to serve as a source of [[activation energy]] to set off the shot. Such loading procedures often require adding paper/cloth [[wadding]] and [[ramrod|ramming down repeatedly with a rod]] to optimize the [[seal (mechanical)|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]] (particularly [[cavalry]] [[charge (warfare)|charge]]s) 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 (rear end) of the barrel, as well as preventing potential propellant loss, contamination or degradation from [[moisture]] and the elements. In modern [[repeating firearm#Autoloading|self-loading firearm]]s, the cartridge case also enables the [[action (firearms)|action]] mechanism to use part of the [[propellant]]'s energy (carried inside the cartridge itself) 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 (firearms)|chamber]] aligned with the [[bore axis]] (i.e. "in ''battery''"). While in the chamber, the cartridge case [[obturation|obturate]]s all other directions except the [[gun barrel#Bore|bore]] to the front, reinforced by a [[breechblock]] or a locked [[bolt (firearms)|bolt]] from behind, designating the forward direction as the [[path of least resistance]]. When the [[trigger (firearms)|trigger]] is pulled, the [[sear (firearm)|sear]] disengages and releases the [[hammer (firearms)|hammer]]/[[firing pin|striker]], causing the [[firing pin]] to impact the [[primer (firearms)|primer]] embedded in the base of the cartridge. The [[shock sensitivity|shock-sensitive]] chemical in the primer then creates a [[jet (fluid)|jet]] of [[spark (fire)|spark]]s that travels into the case and ignites the main propellant charge within, causing the powders to ''[[deflagration|deflagrate]]'' (but not ''[[detonation|detonate]]''). This rapid [[exothermic]] [[combustion]] [[yield (chemistry)|yield]]s a mixture of highly energetic gases and generates a very high [[pressure]] inside the case, often [[fire forming|fire-forming]] it against the chamber wall. When the pressure builds up sufficiently to overcome the fastening [[friction]] between the projectile (e.g. bullet) and the case neck, the projectile will detach from the case and, pushed by the expanding high-pressure gases behind it, [[internal ballistics|move down the bore]] and out the [[muzzle (firearms)|muzzle]] at [[muzzle velocity|extremely high speed]]. After the bullet exits the barrel, the gases are released to the surroundings as [[ejecta]]e in a [[muzzle blast|loud blast]], and the chamber pressure drops back down to [[ambient pressure|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 (firearms)|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.