.45 ACP

The .45 ACP (Automatic Colt Pistol) or 45 Auto (11.43×23mm) is a type of bullet, made to be used in the M1911 pistol used by the U.S. Military. It was first made by John Browning in 1904, the "ACP" in the name stands for "Automatic Colt Pistol". It was the standard for handguns in the U.S. military until they switched to the Beretta M9 (Beretta 92) in 1985 that used a smaller caliber 9mm bullet.
The .45 is famous for being the bullet used in the M1911 and for being the choice of the U.S. Military for their pistols for almost 75 years. The .45 ACP has good stopping power because of the large size of the bullet, a .45 ACP bullet is almost half an inch. When shot at human targets, the .45 ACP bullet makes a big hole that causes blood loss and leads to faster death. 
It was used for guns like the M1911, the Thompson submachine gun, the M3 Grease Gun, the USP45, the UMP45, the TDI Kriss Super V, the MAC-10, and many other guns.