The .45 ACP (Automatic Colt Pistol) or .45 Auto (11.43×23mm)[1]is a rimless straight-walled handgun cartridge designed by John Moses Browning in 1904, 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.[2] The round was developed due to a lack of stopping power in Sulu experienced[3]in the Moro Rebellion using the .38 Long Colt. This experience and the Thompson–LaGarde Tests of 1904 led the Army and the Cavalry to decide a minimum of .45 caliber was required in a new handgun.
