What Does ACP Stand For?

Firearm newcomers generally ask a lot of questions. But if we're honest, between all the firearm lingo and gun jargon, they have a lot of varying terminologies to navigate. Even those who grew up in the firearm culture can confuse all those "alphabet soup" acronyms.

If there's anything we love more than guns and ammo, it's abbreviations for them — and ACP is one of many. You've likely already seen ACP on ammunition boxes and firearms. Although we may recognize those three letters, only some understand their meaning.

Before we dig into what ACP stands for, let's look at the term's roots.

ACP History: Changing the World of Firearms

In 1889, John Browning was shooting with friends when he made a discovery that would ultimately change the course of firearms history. As the men took turns shooting, Browning observed taller grass would bend when his short-statured friend, Will Wright, fired his weapon.

When Wright shot, the muzzle blast would send the grass rippling, indicating a release of energy. This simple observation gave Browning the idea to harness wasted power, working the firearm's action to cycle the next round into the weapon's chamber. At the day's conclusion, Browning had developed a self-loading pistol prototype.

By January 1890, Browning used the inspiration from that first self-loading prototype to file a patent for a gas-operated machine gun. In the next several decades, Browning would file over a dozen more patents for gas and recoil-operated self-loading weapons.

In 1895, Colt Firearms began production of the machine gun Browning had designed, sparking a lengthy collaboration between the two. Although he wasn't the first to develop a semi-automatic pistol, Browning was the first to devise a slide enclosing the firing mechanism and the barrel.

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What Does ACP Stand For?

The short answer is that ACP stands for "Automatic Colt Pistol." However, there's more to it than that.

The letters "ACP" also denote cartridges designed by Browning for Colt semi-automatic pistols. These powerful, highly-accurate rounds have remained popular with sports shooters, military personnel, and tactical forces. ACP's straight-sided cartridges are comparable in appearance and include .25 ACP, .32 ACP, .38 ACP, .380 ACP, and .45 ACP.

.25 ACP

  • Released: 1905

  • Bullet Diameter: .251 inches

  • Case Length: .615 inches

  • Bullet Weight: 30 to 50 grains

Thin and light, the .25 ACP was a versatile round created to compete with the .22 Long Rifle. Because of the cartridge's small dimensions, shooters could load it into some of the most compact weapons ever made.

Unfortunately, the public considered the .25 ACP weakly powered and a poor performer in accuracy. The 1968 Gun Control Act limited the importation of guns of a specific size. Most of these banned guns utilized .25 ACP ammo. By the 1990s, the .25 ACP fell from public use.

.32 ACP

  • Released: 1899

  • Bullet Diameter: .3125 inches

  • Case Length: .680 inches

  • Bullet Weight: 60 to 75 grains

Although released at the end of the 19th century, the .32 ACP became one of the most influential rounds in the 20th century. Designed by Browning and manufactured initially by Fabrique Nationale, it is commonly associated with German police, James Bond, and the historical suicide of Adolf Hitler.

Compact, light, and ideal for concealed carry, police and military forces still use this ammunition worldwide. The .32 ACP offers more velocity than the .32 S&W and can kill small game. However, you must be at close range for the bullet to be effective in self-defense scenarios.

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.38 ACP

  • Released: 1900

  • Bullet Diameter: .356 inches

  • Case Length: 0.9 inches

  • Bullet Weight: 115 to 130 grains

Browning originally designed the .38 (not to be mistaken with the .380 ACP) to pair with the innovative ColtM1900. This pistol was the first to utilize short-recoil operation, now commonly called self-loading.

While the firearm's operating system was game-changing, the cartridge itself was underwhelming. The 1029 development of the .38 Super largely phased out the original, as it offered higher pressure loading. The .38 ACP was loaded in brass, while the .38 Super loads in nickel.

Today, the .38 ACP is rare due to little demand. If you see ammunition labeled as 9X23mm S.R. or .38 Auto, keep in mind that it is the same as .38 ACP. All are semi-rimmed cartridges designed for the ColtM1900.

.380 ACP

  • Released: 1908

  • Bullet Diameter: .355 inches

  • Case Length: .680 inches

  • Bullet Weight: 80 to 120 grains

The .380 ACP ("three eighty") is commonly confused with the .38 ACP ("thirty-eight"). This rimless cartridge has a slightly smaller profile than the .38 but maintains consistent power and performance. The .380 ACP is also known as 9mm Browning, .380 Auto, and 9mm Browning Short.

Historically used for hunting, the .380 ACP is a proven self-defense round popular among military and police forces. Keep in mind, however, that these bullets don't penetrate more than 18 inches. If you plan to use it for home-defense, understand that it performs best at close range (less than three yards).

.45 ACP

  • Released: 1905

  • Bullet Diameter: .452 inches

  • Case Length: .898 inches

  • Bullet Weight: 100 to 230 grain

Browning is, perhaps, best known for creating the ColtM1911, which chambered the .45 ACP. The .45 ACP is a significant reason virtually all manufacturers replicated the 1911.

The .45 is one of the few "ACP" cartridges explicitly created for military purposes. It remains one of the most favored pistol cartridges in the U.S. Used by sports shooters, tactical forces, and military personnel — the .45 ACP round can deliver power and ballistic performance in almost any setting.

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The Colt 1911's Role in The Philippine-American War

When you hear the term "Automatic Colt Pistol," what comes to mind for many is the Colt .45 ACP Model 1911. However, only some realize that Browning designed this weapon and its affiliated .45 ACP ammunition in response to the Philippine-American War.

At the start of the Philippine-American War, U.S. troops carried the Colt M1892 revolver as their designated sidearm. However, the revolver's .38 Colt Long cartridge proved inadequate in incapacitating Moro warriors.

Armed with lethal kris blades in combat, the Moro of the southern islands were tribespeople of incredible physical endurance, fighting ability, and guerilla tactics. Even after being shot several times, they continued charging — prevented blood loss by tying off bleeding limbs.

In 1906, the U.S. military began testing different cartridge and pistol designs for combat use. The duo that emerged as a clear winner was the .45 ACP and Colt Model 1911. The U.S. Army officially adopted both just in time for WWI.

Throughout the Vietnam and Cold War, the U.S. continued to utilize the 1911. In 1985, the Beretta M9 replaced Colt's M1911. However, due to its popularity, the 1911 was never completely phased out of military use.

Today's Colt Model 1911

Some say nostalgia and a wildly committed fan base contribute to the 1911's popularity today. However, given the modern advances in small arms technologies, there is more to the 1911 / .45 ACP duo that helps maintain the appeal.

First, the 1911 and .45 ACP combination delivers significant stopping power. Although the cartridge produces some lumbering velocities, the projectiles are large and heavy. Their bulk has serious, hard-hitting kinetic energy, penetrating deep and cutting wide.

Second, the recoil is relatively tame for such a large caliber. Many claim it produces less perceived recoil than many lightweight .40 S&W pistols. The 1911's bulk certainly helps absorb some of that recoil.

Finally, the 1911 makes a practical carry weapon. Even though the Government's 1911 model measures 9 inches and weighs a hefty 3 pounds, the slide is relatively slim. Measuring .9 inches, the 1911 is significantly more slender than a Glock 17's 1.26 inches. That thin profile makes even the largest 1911 surprisingly easy to carry.

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