Nothing, .45 auto is just another name for .45ACP.
Both can refer to 45ACP. 45 alone can also refer to 45 Colt
.45 auto and .45ACP are the same round.
The glock 21 fires the .45 automatic colt pistol (.45acp, or .45 auto) round.
The .45 GAP was developed by an engineer with CCI/Speer, commissioned by Glock, to be a smaller round with the same power as a .45ACP. This was achieved essentially with powder selection. The .45 GAP has the same diameter as the .45 ACP but the case is shorter, it uses small pistol primers, and is designed for higher standard pressure to make it on par with the terminal velocity of the .45ACP round. To compensate for this increase in pressure the round has a stronger case head to prevent case head blowouts. The .45 GAP stands for "Glock Automatic Pistol" and is the first cartridge associated exclusively with Glock. The .45 GAP and the .45ACP are completely different rounds that are not interchangeable, although they perform similarly.
Nothing, two names for the same round.
Nothing, two names for the same round.
The Model 1911 is a semi-automatic pistol chambered in .45ACP. The Model 1917 is a large frame revolver also chambered in .45ACP but using half-moon or full-moon clips to hold the rounds.
The 45 long colt has a longer rimmed case and is used in revolvers and rifles. The 45ACP has no rim, is shorter and is used in automatic pistols. They share the same bullets but the cases and powder charges are different. You can't interchange the two.
The 45 long colt has a longer rimmed case and is used in revolvers and rifles. The 45ACP has no rim, is shorter and is used in automatic pistols. They share the same bullets but the cases and powder charges are different. You can't interchange the two.
If the question you are asking is about a colt model 1911 semi-auto 45acp? then with that serial number your colt was a commercial model made in 1916.
It is the named of the cartridge it shoots- the .45 Automatic Colt Pistol cartridge.