.25 ACP

The .25 ACP (Automatic Colt Pistol), also known as the .25 Auto, .25 Automatic, or 6.35×16mmSR) is a semi-rimmed, straight-walled centerfire pistol cartridge introduced by John Browning in 1905 alongside the Fabrique Nationale M1905 pistol.

Design
The cartridge is of semi-rimmed design meaning that the rim protrudes slightly beyond the diameter of the base of the cartridge so the cartridge can headspace on the rim.

Though the .25 ACP was designed for semi-automatic pistols, various .25 ACP revolvers were produced in the early twentieth century by Belgian, French, and German gunmakers such as Adolph Frank and Decker. In the late twentieth century, Bowen Classic Arms produced a custom Smith & Wesson revolver in .25 ACP.

Performance
The use of the .25 ACP allows for a very compact lightweight gun, usually pocket pistol. With quality ammo available on the market, the .25 ACP is viewed by some as a solid choice for personal defense handguns due to its centerfire-case design, which is inherently more reliable than a .22 LR rimfire cartridge.