Yup, you are correct. .45ACP and .45 Auto are the same round. Not to be confused with .45GAP, as you pointed out, or .45 Auto Rim.

Thanks Mike!!!
Just wanted to be sure!!!

My sister went in wal mart to buy me some 45acps as gift. Clerk told her they didn't sell 45acp, only 45 auto.

45Automatic Colt Pistol.

http://en.wikipedia.org/wiki/45_ACP

There's also .45 Long Colt, usually called ".45 Colt." That might be the same as .45 auto rim...Mike, please share your wealth of knowledge.

Originally Posted by fivehourfrenzy

There's also .45 Long Colt, usually called ".45 Colt." That might be the same as .45 auto rim...Mike, please share your wealth of knowledge.

Not the same as .45 auto rim. I don't know if a revolver chambered in .45 colt will also fire .45 auto rim. My guess would be yes, but that is only a guess.

The .45 auto rim was created specifically for the M1917 revolver, even though that revolver was designed specifically for the .45ACP cartridge. The M1917 became popular with civilians in the 20s and the .45 auto rim was made to chamber in the guns to save having to use half-moon clips and to save the barrels' lives being shortened by the jacketed bullets.

More reading on that here.

Actually, the proper name for the old revolver cartridge is ".45 Colt" rather than ".45 Long Colt."

I'm not absolutely sure, but I believe that the .45 "Long" Colt's case was originally bore diameter, holding a "heeled" bullet. The .45 Auto-Rim cartridge is larger than bore diameter, and thus would be too large to chamber in a .45 "Long" Colt cylinder. Conversely, the .45 "Long" Colt cartridge would be somewhat smaller than a .45 ACP revolver's chamber, and may explosively expand to fit upon firing, which wouldn't be a good thing.

The .45 "Long" Colt is informally so named to distinguish it from the Government-Issue .45 revolver cartridge of the Indian Wars, which was somewhat shorter in both case and overall length. The reason for the shorter .45 case was that it would fit both the Colt SA and the Smith & Wesson SA revolver in use at the time. The S&W had a shorter cylinder than the Colt, and the government's .45 "Short" cartridge fit both.

Originally Posted by forestranger

My sister went in wal mart to buy me some 45acps as gift. Clerk told her they didn't sell 45acp, only 45 auto.

I'm surprised she could even find someone there. I find it impossible to find those highly trained individuals wearing the tan vest.

Originally Posted by Todd

I'm surprised she could even find someone there. I find it impossible to find those highly trained individuals wearing the tan vest.

Yeah I asked for "forty smith and wesson" one time and they said they had .40, but only in Winchester, not S&W. Another time I went in and tried to buy some CCI mini-mags in .22LR and they gave me a super concerned look and said, "um, sir, we don't sell BULLETS after hours. You're gonna hafta come back during the DAY if you want to buy BULLETS." Yeah, like I'm gonna go on a full-blown assault with a .22.

Originally Posted by Steve M1911A1

I'm not absolutely sure, but I believe that the .45 "Long" Colt's case was originally bore diameter, holding a "heeled" bullet. The .45 Auto-Rim cartridge is larger than bore diameter, and thus would be too large to chamber in a .45 "Long" Colt cylinder. Conversely, the .45 "Long" Colt cartridge would be somewhat smaller than a .45 ACP revolver's chamber, and may explosively expand to fit upon firing, which wouldn't be a good thing...

Wrong, wrong, wrong!
I got it exactly the wrong way 'round.
I looked it up in Townsend Whelen's Why Not Load Your Own, and found that the .45 ACP (and Auto-Rim) case is 0.471" O.D. (bullet 0.450"/0.451"), and the .45 "Long" Colt case is 0.476" O.D. (bullet 0.453").
Not that it's important, but I like to post accurate information (when I can't seem to keep my stupid mouth shut).
Sorry 'bout that...