Caliber

Question
What does ACP stand for when listed after pistol caliber?  Thank You, Jerry

Answer
Jerry,

Many calibers have some sort of designation with them besides thier diameter in inches (e.g. .357,. 45, etc., such as "Magnum" or "S&W".

In the early 1900's John Browning was experimenting with the design for an auto pistol that was the forerunner of the 1911.

This pistol was variously chambered, but always in something that started with a "3".

Browning entered into a deal with Colt, as they were trying to win a government contract for a new military pistol.

The government, underwhelmed with the success that pistols beginning with a "3" were having, had found great success with a .45 in their old Single Action Army revolvers.

But there was no .45 cartridge for an auto pistol, so John Browning was tasked to invent one.

The US Military adopted the gun in 1911 (hence the name, Model 1911), and ordered a number of them from Colt, with it's newly designed and produced cartridge, the .45ACP, which stands for "Automatic Colt Pistol."