In 1905, the .45 Automatic Colt Pistol (ACP) was designed by John Moses Browning (1855-1926). The ammo was created for a prototype of the Colt M1911 semi-automatic pistol.  Browning intended the ammo for use in the U.S. military, but the .45 ACP is revered by civilians, mostly for sports shooting and self-defense. Competition shooters often choose the ammo for its high level of accuracy and mild recoil.

Development

In 1904, Colt had been working alongside Browning to develop a .41 caliber cartridge. In 1905, the Cavalry approached Colt to create a .45 caliber equivalent. Colt modified its pistol design to accommodate an enlarged version of the .41 round. Colt met the request with the Model 1905 and the .45 ACP cartridge. The original round went through a series of changes but eventually used the following specs: 230-grain bullet with a velocity of 850 ft/s.

By 1906, six manufacturers, including Colt, submitted prototypes to the military. Colt submitted Browning’s design along with prototypes from Sage and DWM – all were accepted. DWM, who had submitted two Parabellum P08s chambered with .45 ACP, withdrew from testing for unknown reasons. After completing a series of military trials, Browning’s .45 ACP was adopted as the standard ammunition for Colt’s M1911 pistol.

Military

Although the .45 ACP was designed by Browning and produced by Colt, the most influential person in choosing the new ammunition was Army Ordnance Board member General John T. Thompson, developer of the Thompson submachine gun. Thompson asked weapons manufacturers to create a bigger bullet to be chambered in a “real man-stopper.” Thompson saw the inadequate performance of the Army’s .38 Long Colt pistols during the Philippine–American War (1899–1902). He insisted that the Army needed a more powerful weapon. As a result, the military adopted the .45 Auto.

Law Enforcement

While many law enforcement agencies have stopped issuing the .45 as standard ammunition, there are some that continue to use it for its stopping power. Agencies include the Los Angeles Police Dept. SWAT and the FBI’s Hostage Rescue Team (HRT). Despite the fact that the U.S. military switched over to 9mm in 1985, Delta Force and certain United States Special Ops Command can still choose to use the .45 in their pistols.

Performance

The .45 ACP is an excellent combat pistol ammunition cartridge that combines high level accuracy and stopping power. It has a low muzzle flash and produces moderate recoil in handguns; compact models have a higher recoil. The military’s standard issue .45 ACP ammo uses a 230-grain bullet that travels 830 FPS when fired from the M1911A1 pistol; 950 FPS from the M1A1 Thompson submachine gun. The ammo also comes in specialty rounds of varying performance levels and weights.

Compared to similar rounds, it has a relatively low maximum chamber pressure of 21,000 PSI. The 9mm Parabellum has a pressure of 35,000 PSI, the .40 S&W has a pressure rating of 37,500 PSI, and the 10mm Auto has a pressure rating of 40,000 PSI. Lower pressure saves the weapon from excessive wear and tear, prolonging its life.

Self-Defense

When it comes to self-defense, many civilians choose the .45 Auto because of its stopping power. The bullet has deep penetration and creates a wound able to damage the central nervous system, circulatory system, and critical organs. While the .45 ACP may be too much for the job at hand, the .45 ACP remains popular because it is one of the most iconic guns out there thanks to iconic movies and pop culture. A 9mm or even a .22mm could be enough for self-defense but some still seek the accuracy and surefire reputation of the .45 ACP.

The stopping power is the main reason most people choose to use a .45. It’s one reason that law enforcement agencies, including the FBI’s Hostage Rescue Team (HRT) and the Los Angeles Police Department SWAT, continue to use it out in the field.

It’s easy to understand that people want to protect their homes and families. With that in mind, choosing a .45 ACP ammo makes sense. After all, the purpose of home defense is to stop the threat. But that doesn’t always mean shoot to kill. It can mean wounding the intruder or scaring him off. Before choosing a high-powered round, users should be aware that its deep penetration can cause injury to other people or property outside the intended target.

Alternate Names

• 45
• .45 Rimless Smokeless
• .45 Auto
• .45 Auto. Colt / .45 AC (Winchester)
• .45 M1911 (U.S. Military)
• S.A. .45-inch (British Commonwealth Military)