The .45 ACP (Automatic Colt Pistol), or .45 Auto (11.43×23mm) is a handgun cartridge designed by John Browning in 1905, for use in his prototype Colt semi-automatic pistol. After successful military trials it was adopted, along with the Browning .45 Colt handgun, as the .45 M1911 cartridge. The handgun was designated M1911 handgun