The ACP stands for the Automatic Colt Pistol and the GAP stands for the Glock Automatic Pistol. The 45 GAP has a smaller grip than the 45 ACP however; the affordability and the availability for both differ as well. 45 ACP (.45 ACP) The ACP cartridge was introduced in 1904 for use by the military from year 1911.Is .45 ACP the same as .45 Auto?
Contrary to popular belief, the 45 Auto and 45 ACP are one and the same. You don't have to wonder if you're looking at the correct ammunition for your gun. Many manufacturers assign different designations to their cartridges. But that doesn't mean that there are any core technical differences between 45 Auto and 45 ACP rounds.