The 45 ACP (Automatic Colt Pistol) or 45 Auto (11.43×23mm) 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. The round was developed due to a lack of stopping power in Sulu experienced 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.