ACP stands for "Automatic Colt Pistol" and refers to cartridges designed by John Moses Browning for Colt semi-automatic pistols. These cartridges are straight-sided and include .25 ACP, .32 ACP, .38 ACP, .380 ACP, and .45 ACP. The .45 ACP is one of the most well-known ACP cartridges and was developed by Browning in 1904 for use in his prototype Colt semi-automatic pistol. It was adopted as the standard chambering for Colts M1911 pistol after successful military trials. The ACP cartridges are not used in revolvers or rifles, but are exclusively used in pistols.