Cylinder (firearms)

In firearms, the cylinder is the cylindrical, rotating part of a revolver containing multiple chambers, each of which is capable of holding a single cartridge. The cylinder rotates (revolves) around a central axis in the revolver's action to sequentially align each individual chamber with the barrel bore for repeated firing. Each time the gun is cocked, the cylinder indexes by one chamber (for five-shooters, by 72°, for six-shooters, by 60°, for seven-shooters, by 51.43°, for eight-shooters, by 45°, for nine-shooters, by 40°, and for ten-shooters, by 36°). Serving the same function as a rotary magazine, the cylinder stores ammunitions within the revolver and allows it to fire multiple times before needing to reload.

Typically revolver cylinders are designed to generally hold six cartridges (hence revolvers sometimes are referred to as "six-shooters"), but some small-frame concealable revolvers such as the Smith & Wesson Model 638 have a 5-shot cylinder, due to the smaller overall size and limited available space. The Nagant M1895 revolver has a 7-shot cylinder, the Webley-Fosbery Automatic Revolver has an 8-shot cylinder in .38 caliber, and the LeMat Revolver has a 9-shot cylinder. Several models of .22 rimfire-caliber revolvers have cylinders holding 9 or 10 rounds.

As a rule, cylinders are not designed to be detached from the firearm (except for cleaning). Rapid reloading is instead facilitated by the use of a speedloader or moon clip, although these work only on top-break and swing-out cylinder revolvers; revolvers having fixed cylinders must be unloaded and loaded one chamber at a time.