what is the difference between .45 acp and .45 auto
.45 ACP The .45 ACP (Automatic Colt Pistol), or .45 Auto (11.43Ã—23mm)[1] 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 as the standard chambering for Colt's M1911 pistol, being named .45 ACP.[2]