CALIBER

ACP stands for Automatic Colt Pistol. So when you see ".45 ACP," it means a .45-caliber cartridge originally designed for semi-automatic pistols. It is also sometimes referred to as .45 Auto. You may also see it condensed as “45ACP.”

The .45 ACP is known for its historical legacy, heavy bullet weight, and hard-hitting force. It was the cartridge chambered in the 1911 during both World Wars, and it remains a go-to for 1911 enthusiasts and self-defense shooters alike. Manufacturers continue to produce it in both full metal jacket (FMJ) and defensive hollow point loads. While it delivers strong recoil, it is still regarded as one of the most controllable defense rounds available.

Yes. .45 ACP and .45 Auto are the same cartridge. The names are used interchangeably, with .45 ACP being the more traditional designation and .45 Auto appearing on some modern ammunition packaging.

Typically, yes. The .45 ACP is a slow-moving bullet that usually travels below the speed of sound, making it naturally subsonic. That characteristic makes it a popular choice for suppressed shooting. Without breaking the sound barrier, you do not get the supersonic crack, just the mechanical sound of the firearm itself.

Yes. The .45 ACP has a significantly larger bullet diameter than the 9mm, which is part of why it is known for its wound channel size and being less likely to overpenetrate its target. The .45 ACP's heavier, wider bullet delivers the largest bullet expansion of common defensive handgun rounds.

Rock Island Armory chambers several pistols in .45 ACP, spanning the full lineup from classic GI-style 1911s to competition-ready models. Browse the full .45 ACP firearm collection at armscor.com/45acp.