The 45 ACP (45 Auto) was designed by John Browning in 1905 for his prototype semiautomatic pistol that eventually became the legendary Colt 1911, using a .452-inch bullet. Browning proposed a 200-grain bullet; U.S. Army Ordnance, smarting from reports of poor performance of the 38 Long Colt in the Philippines, increased bullet weight to 230 grains for greater stopping power...and the 45 ACP as it is today was adopted in 1911. It remains an iconic and popular handgun cartridge for personal defense and competition, and was used by the U.S. military in submachine guns (Thompson and M3) through the 1970s. Although largely replaced by the 9mm for military use and the 9mm and/or 40 S&W in the law enforcement community, the 45 ACP is still used by the U.S. military and numerous law enforcement agencies in various applications. The standard load remains a 230-grain bullet at 780 to 850 fps, but lighter, faster bullets from 165 to 200 grain, delivering a bit less recoil, are also available.
