Development Of The Colt 45 Acp

The Colt automatic pistol design is still manufactured.

Automatic Colt Pistol, ACP, identifies the type of ammunition used in the Colt automatic pistol. Colt developed the Model 1911 handgun and its .45-caliber Automatic Colt Pistol ammunition at the Army’s request to replace the .38-caliber pistols they were using.


Colt was developing an automatic pistol with the ACP concept in smaller calibers. They had been working on a .41-caliber pistol when the U. S. Army requested a .45-caliber pistol in 1905. Browning made the .41-caliber cartridge for the Colt-designed automatic pistol. Browning modified the .41-caliber cartridge to .45 caliber and further refined the design.

Colt Model 1911

Several companies submitted bids for the Army’s new pistol. Some dropped out, while others had performance problems, which left Colt to supply the pistols. The Army requested tests to determine the bullet weight and powder load for the cartridge.


The Army, on March 29, 1911, accepted the Colt Model 1911 handgun with .45-caliber ACP ammunition for production. It proved a reliable and accurate side arm, and was used throughout most of the twentieth century. The U. S. military switched to the nine-millimeter Beretta 92F on January 14, 1985 in order to standardize sidearm ammunition with its NATO allies. Law enforcement, civilian shooters and other military forces still use .45-caliber ACP ammunition in a variety of handguns, including the currently-manufactured version of the Colt Model 1911.