look up any word, like hipster:
 
1.
ACP = Auto Colt Pistol

The legendary, and common, caliber, used in handguns of wide varieties. The .45acp cartridge was chambered in the legendary Colt M1911A1 handgun, used by american infantry during WWII.

.45acp is used even today, for such guns like the H&K Mark 23 SOCOM, and H&K's USP's. .45acp is even the caliber for the Tommygun used in WWII, and today it is used in H&K's UMP submachine gun.
".45acp is powerful too. ^_^"
-me
by Dave February 03, 2004