Editing Cartridge (firearms) (section)

==Semi-automatic vs. revolver cartridges==
Most [[revolver]] cartridges are rimmed at the base of the case, which seats against the edge of the [[cylinder (firearms)|cylinder]] [[chamber (firearms)|chamber]] to provide [[headspace (firearms)|headspace]] control (to keep the cartridge from moving too far forward into the chamber) and to facilitate easy extraction.

Nearly every [[centerfire]] [[semi-automatic pistol]] cartridge is "rimless", where the rim is of the same diameter as the case body but separated by a circumferential groove in between, into which the [[extractor (firearms)|extractor]] engages the rim by hooking. A "semi-rimmed" cartridge is essentially a rimless one but the rim diameter is slightly larger than the case body, and a "rebated rimless" cartridge is one with the rim smaller in diameter. All such cartridges' headspace on the case mouth (although some, such as [[.38 Super]], at one time seated on the rim, this was changed for accuracy reasons), which prevents the round from entering too far into the chamber. Some cartridges have a rim that is significantly smaller than the case body diameter. These are known as rebated-rim designs and almost always allow a handgun to fire multiple caliber cartridges with only a barrel and [[magazine (firearms)|magazine]] change.
<gallery mode="packed">
File:380 ACP - FMJ - SB - 2.jpg|Rimless [[.380 ACP]] semi-automatic cartridge
File:38 Special - FMJ - SB - 2.jpg|Rimmed [[.38 special]] revolver cartridge
</gallery>