What is ACP Ammo? And When Should You Use It? The Full Guide!

There are many abbreviations and terms in the gun and ammunition world. CCW, for example, stands for “Carrying Concealed Weapon,” and it usually serves as the catchall abbreviation to describe someone with a license to carry a concealed handgun. Another abbreviation we frequently see in the gun world is “ACP,” as in “His pistol is a 1911 that takes .45 caliber ACP ammunition.” In this case, we know that the pistol is a 1911-style semiautomatic handgun that fires a .45 caliber ACP ammunition cartridge. But what is ACP ammo? Let’s find out.

45 ACP Cartridges

It References Colt

“ACP” refers to the legendary American gun maker Colt Firearms and the ammunition John Browning designed for the company between 1900 and 1908. In 1900, Colt introduced the Colt Model 1900, its first semiautomatic pistol, which the company called an “automatic pistol.” The ammunition needed for Colt’s “automatic pistols” was named ACP, or “Automatic Colt Pistol.”

Why New Ammunition?

Colt’s new handguns were considered revolutionary for the era, as was their ammunition, and here’s why:

  • The Colt M1900 was semiautomatic. Once you prepared the handgun to fire its first round, all you had to do to fire another was pull the trigger.
  • Before you pulled the trigger, though, you had to prepare the weapon to fire, first by loading your ammunition into the gun.
  • To make Colt’s new “automatic pistol” ready to fire, you had to pull its slide back and then release it. Pulling back and releasing the 1900’s slide inserted a cartridge into its firing chamber.
  • Once you’d made the M1900 ready to fire — which also cocked the hammer back and locked it into the firing position — you could then shoot it.
  • After you pulled your gun’s trigger, the Automatic Colt Pistol or ACP cartridge in its firing chamber would ignite and fire a bullet out of the gun’s barrel.
  • The “automatic” feature of this now-historic semiauto pistol is that it automatically loaded, or “autoloaded,” a new cartridge into its firing chamber, one after the other after each trigger pull until it ran out of ACP ammo from its internal magazine.
  • Modern semiautomatic handguns continue to work on the same basic principles the Colt M1900 and the timeless M1911 used back in the early 1900s.

Cocked Hammers

Unlike with a revolver, Colt’s new semiautomatic handguns also automatically cocked their hammers after their first slide pull. This “automatic” trigger cocking feature of the gun maker’s new semiautomatic handguns was also innovative because revolvers didn’t automatically cock their triggers. Colt “automatic pistols” and their creative loading and reloading, hammer locking, and firing features were all designed to work as a system with their new ACP ammo.

Ammo Specificity

The new Colt autoloaders were indeed formidable weapons. As fast as you could pull the M1900’s trigger, you could fire a round. For such an impressive handgun to work correctly, though, it did require a new type of ammunition, the Automatic Colt Pistol or ACP cartridge. John Browning designed this ammunition to precisely fit into the new Colt “automatic pistols.” The handgun required the ammunition’s precise fit to ensure everything functioned correctly and with little chance of misfiring or other issues.

ACP Ammo Pros

ACP ammo has more than a few advantages or pros, including:

  • ACP ammo is common, and prices for it are generally reasonable.
  • ACP comes in several different calibers, including: .25 ACP, .32 ACP, .380 ACP, and .45 ACP.
  • .25 ACP and .380 ACP are very popular cartridges for use in subcompact, easily concealable, semiautomatic handguns.
  • .45 ACP is one of the two most popular ammunition cartridges for full-size semiautomatic pistols. A .45 caliber bullet is a big round, and it has excellent knockdown or stopping power.

ACP Ammo Cons

There are few cons regarding ACP ammunition. Today, this venerable and well-known ammo fits many non-Colt handguns. It is more known for its different calibers or sizes than anything directly related to its construction. What cons do exist when it comes to ACP have more to do with their calibers and those rounds’ performance than anything else. For example:

  • Perceived recoil from a .45 ACP round may be noticeable. Such recoil may be a bit too much for some shooters to handle.
  • By contrast, a .380 ACP round may not have the knockdown or stopping power needed to end a threat.

The above “cons” are just minor quibbles that I may have as a longtime gun owner and shooter. When ACP ammunition is in a handgun designed to take it, it performs reliably and competently and in a variety of environmental and tactical conditions.

It’s Part of a System

With all the above information, it should now be easy to answer, “What is ACP ammo?” However, as with all ammunition, keep in mind that ammo is just part of a system consisting of your handgun and even your holster. You are also an essential part of that system. “It’s about the shooter, not the gun,” in other words.

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