The .45 ACP (11.43Ã23mm) (Automatic Colt Pistol), also known as the .45 Auto by C.I.P., is a cartridge designed by John Browning in 1904, for use in his prototype Coltsemi-automatic .45 pistol and eventually the M1911 pistoladopted by the United States Army in 1911.[2]
Quoted from Wikipedia...