You can fire a .45 ACP cartridge through a .45 ACP pistol - and only a .45 ACP pistol. The various .45 cartridges (.45 ACP, .45 Long Colt, .45 GAP, etc.) are not interchangeable with each other.

ACP means Automatic Colt Pistol. .45 ACP and .45 Auto are the same cartridge. .45 Colt and .45 Auto Rim are a revolver cartridge. .45 GAP (Glock Auto Pistol) is a shorter round than the ACP, and does not interchange with it.

ACP stand for Automatic Colt Pistol

.45 ACP means Automatic Colt Pistol. It IS .45 Auto.

No. The 45 ACP (which means 45 Auto) cannot use the .45 GAP or the .45 Magnum.