Editing Cartridge (firearms) (section)

==== Case ====
[[Image:Many bullets.jpg|thumb|Three non-bottlenecked cartridges ([[9×19mm Parabellum]], [[.40 S&W]] and [[.45 ACP]]) on the left, three bottlenecked cartridges ([[FN 5.7×28mm]], [[5.56×45mm NATO]] and [[.300 Winchester Magnum]]) in the center, and two [[polymer-cased ammunition|polymer-cased]] [[12-gauge]] [[shotshell]]s on the right]]
The main defining component of the cartridge is the case, which gives the cartridge its shape and serves as the integrating [[housing (engineering)|housing]] for other functional components, it acts as a container for the propellant powders and also serves as a protective [[shell (structure)|shell]] against the elements; it attaches the projectile either at the front end of the cartridge ([[bullet]]s for [[pistol]]s, [[submachine gun]]s, [[rifle]]s, and [[machine gun]]s) or inside of the cartridge ([[wadding]]/[[sabot (firearms)|sabot]] containing either a quantity of [[shot (pellet)|shot (pellets)]] or an individual [[shotgun slug|slug]] for [[shotgun]]s), and align it with the [[gun barrel#Bore|barrel bore]] to the front; it holds the [[primer (firearms)|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 [[cartridge paper|paper]] had been used in the [[paper cartridge|earliest cartridges]], almost all modern cartridges use [[metallic cartridge|metallic casing]]. The modern metallic case can either be a "bottleneck" one, whose frontal portion near the end opening (known as the "case ''neck''") has a noticeably smaller [[diameter]] than the main part of the case ("case ''body''"), with a noticeably angled slope ("case ''shoulder''") in between; or a "straight-walled" one, where there is no narrowed neck and the whole case looks [[cylindrical]]. The case shape is meant to match exactly to the [[chamber (firearms)|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" which has 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 [[crimp (joining)|crimping]], is known as the ''{{vanchor|case mouth}}''. The closed-off rear end of the case body, which holds the [[primer (firearms)|primer]] and technically is the case ''base'', is called the ''case head'' as it is the most prominent and frequently the widest part of the case. There is a circumferential [[flange]] at the case head called a ''[[rim (firearms)|rim]]'', which provides a lip for the [[extractor (firearms)|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 (e.g. body diameter, shoulder slant angle and position, and neck length) also affects the amount of attainable pressure inside the case, which in turn influences the [[accelerative]] capacity of the projectile. [[Wildcat cartridge]]s are often made by reshaping the case of an existing cartridge. Straight-sided cartridges are less prone to rupturing than [[Tapering (firearms)|tapered cartridges]], in particular with higher pressure propellant when used in blowback-operated firearms.

In addition to case shape, [[rifle cartridge]]s can also be grouped according to the case dimensions of a cartridge, this is usually referring to the cartridge's overall length (COL), which in turn dictates the minimal [[receiver (firearms)|receiver]] size and operating space ([[bolt (firearms)|bolt]] travel) needed by the [[action (firearms)|action]], into either "mini-action", "short-action", "long-action" ("standard-action"), or "[[magnum cartridge|magnum]]-action" categories.
* ''Mini-action'' cartridges are usually [[intermediate cartridge|intermediate rifle cartridges]] with a COL of {{cvt|2.25|in|lk=on|order=flip}} or shorter in length, which is most commonly exemplified by the [[.223 Remington]];
* ''Short-action'' cartridges are usually [[fully powered cartridge|full-powered rifle cartridge]]s with a COL between {{cvt|2.25|and|2.8|in|order=flip}}, which is most commonly exemplified by the [[.308 Winchester]];
* ''Long-action'' ("standard-action") cartridges are usually traditional full-powered rifle cartridges with a COL between {{cvt|2.8|and|3.34|in|order=flip}}, 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 {{cvt|3.34|and|3.6|in|order=flip}}, including some of the long-action cartridges with a case head larger than {{cvt|.50|in|order=flip}} diameter, which is most commonly exemplified by the [[.375 Holland & Holland Magnum]].<ref>{{cite web|url=https://blog.gunassociation.org/short-action-vs-long-action-rifles/|title=Short Action vs Long Action Rifles Explained|last=|first=|date=3 August 2020|publisher=American Gun Association|access-date=1 February 2021|archive-date=18 January 2021|archive-url=https://web.archive.org/web/20210118134927/https://blog.gunassociation.org/short-action-vs-long-action-rifles/|url-status=live}}</ref>

The most popular material used to make cartridge cases is [[brass]] due to its good [[corrosion resistance]]. The head of a brass case can be work-hardened to withstand the high pressures, and allow for manipulation via extraction and ejection without rupturing. The neck and body portion of a brass case is easily annealed to make the case [[ductile]] enough to allow reshaping so that it can be [[handloading|handloaded]] many times, and [[fire forming]] can help [[accurize]] the shooting.

Steel casing is used in some [[plinking]] ammunition, as well as in some military training ammunition (mostly from the [[former Soviet republics]] of Armenia, Azerbaijan, Belarus, Estonia, Georgia, Kazakhstan, Kyrgyzstan, Latvia, Lithuania, Moldova, Russia, Tajikistan, Turkmenistan, Ukraine, and Uzbekistan), along with Russia and China.{{Citation needed|date=September 2018}} 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 rifle|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 [[Military logistics|logistic]] advantage.<ref>{{Cite web |title=Mass, Weight, Density or Specific Gravity of Different Metals |url=https://www.simetric.co.uk/si_metals.htm |access-date=2022-11-07 |website=www.simetric.co.uk |archive-date=31 December 2018 |archive-url=https://web.archive.org/web/20181231175853/https://www.simetric.co.uk/si_metals.htm |url-status=live }}</ref> 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 leak into the chamber. Constituents of these gases condense on the (relatively cold) 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 [[engineering tolerance|tolerance]]s than [[NATO]] weapons.{{Citation needed|date=September 2018}}

Aluminum-cased cartridges are available commercially. These are generally not reloaded, as aluminum [[fatigue (material)|fatigue]]s easily during firing and resizing.  Some calibers also have non-standard primer sizes to discourage reloaders from attempting to reuse these cases.

{{missing information|semi-combustible cases in [[120×570mm NATO]] tank shells: the body is polymer, but the base stays|date=March 2023}}
[[Polymer-cased ammunition|Plastic cases]] are commonly used in [[shotgun shell]]s, and some manufacturers offer [[polymer]]-cased [[centerfire]] pistol and rifle cartridges.<ref>Johnson, S. (2013, January 10). Extreme polymer research’s polymer handgun cartridge cases -. The Firearm Blog. https://www.thefirearmblog.com/blog/2011/09/23/extreme-polymer-researchs-polymer-handgun-cartridge-cases/ {{Webarchive|url=https://web.archive.org/web/20240204035450/https://www.thefirearmblog.com/blog/2011/09/23/extreme-polymer-researchs-polymer-handgun-cartridge-cases/ |date=4 February 2024 }}</ref><ref>Beckstrand, T. (2018, October 16). True velocity’s new polymer-cased ammunition. Guns and Ammo. https://www.gunsandammo.com/editorial/true-velocitys-new-polymer-cased-ammunition/247607 {{Webarchive|url=https://web.archive.org/web/20240204035450/https://www.gunsandammo.com/editorial/true-velocitys-new-polymer-cased-ammunition/247607 |date=4 February 2024 }}</ref>