Cartridge (firearms) - Semi-automatic Vs. Revolver Cartridges

Semi-automatic Vs. Revolver Cartridges

Most revolver cartridges have a rim at the base of the case that is larger than the case body is and which seats against or into the cylinder block to provide headspace control (to keep the cartridge from moving too far forward in the cylinder chamber) and to provide for easy extraction.

Nearly every semi-automatic pistol cartridge is “rimless,” or more precisely has a rim of the same diameter as the case body. An extractor engages this rim by entering a cannelure near the base of the case. A few designs, known as "semi-rimmed" have a rim that is slightly larger than case body diameter but these function as a rimless design. 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 cartidges have a rim that is significantly smaller than 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 change.

For a visual comparison of similar-diameter handgun cartridges with different rim designs, see 380 ACP (semi-automatic) vs. .38 Special (revolver.)

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