.45 ACP History Print E-mail

Design & History

The US Cavalry had been buying and testing various handguns in the late 1890s and early 1900s. The .45 Colt Single Action Army had largely been replaced, even by some double action versions of the same. The Cavalry had fielded some double action revolvers in .38 Long Colt, and they determined that the .38 caliber round was significantly less effective against determined opponents, such as those encountered in the Moro Rebellion warriors they were fighting at the time, than the .45 Colt. The current issue rifle at the time, the .30-40 Krag, also had failed to stop Moro warriors[1]; the British had similar issues switching to the .303 British, which resulted in the development of the Dum-dum bullet. This experience, and the Thompson-LaGarde Tests of 1904 led the Army and the Cavalry to decide that a minimum of .45 caliber was required in the replacement handgun.
Colt had been working with Browning on a .41 caliber cartridge in 1904, and in 1905 when the Cavalry asked for a .45 caliber equivalent Colt modified the pistol design to fire a .45 caliber version of the prototype .41 caliber round. The result from Colt was the Colt Model 1905 and the new .45 ACP. The original round that passed the testing fired a 200 grain (13 g) bullet at 900 ft/s (275 m/s), but after a number of rounds of revisions between Winchester Repeating Arms, Frankford Arsenal, and Union Metallic Cartridge, it ended up using a 230 grain (15 g) bullet at about 850 ft/s (260 m/s). The resulting .45 caliber cartridge, named the .45 ACP, is similar in performance to the .45 S&W cartridge, and only slightly less powerful (but significantly shorter) than the .45 Colt cartridges the Cavalry was using. The cartridge case shared the same head dimensions as the .30-03 and later .30-06 rifle cartridges in use by the military at the time.

By 1906 bids from 6 makers were submitted, among them Browning's design, submitted by Colt. Only DWM, Savage, and Colt made the first cut. DWM, which submitted two Luger pistols adapted to the .45 ACP cartridge, withdrew from testing after the first round of tests, for unspecified reasons.[2] One of the DWM pistols, serial number 1, was destroyed in testing; the remaining instance, serial number 2, is considered one of the most desirable collectors handguns in existence[3].

In the second round of testing in 1910, the Colt design passed the extensive testing with no failures, while the Savage design suffered 37 stoppages or parts failures.[4] The resulting design was adopted as the Model 1911.


The result is one of the world's more effective combat pistol cartridges, one that combines very good accuracy and stopping power for use against human targets. The cartridge also has relatively low muzzle blast and flash, as well as moderate recoil. Like many pistol cartridges, it is a low-velocity round, and thus not particularly effective against body armor. Another drawback for large scale military operations is the cartridge's large size, weight, the increased material cost of manufacture compared to the 9 mm Parabellum cartridge, and lack of compliance with Standardization Agreements pertaining to handgun ammunition currently enacted between the US and many of its allies.

Even in its non-expanding full metal jacket (FMJ) version, the .45 ACP cartridge has a reputation for effectiveness against human targets because its large diameter creates a deep and substantial permanent wound channel, although some writers, such as the published work of Marshall and Sanow, have cast the reputation of .45 ACP being the "best" at this task into doubt. Although there has been some doubt cast on the work itself, the Marshall and Sanow work remains the standard of modern thought on ballistic performance.

Over the past few decades, modern hollow-point configurations have appeared in an attempt to increase the expansion potential and lethality of the round. Unfortunately, given the .45 ACP's relatively low speed (in the 850 fps range), expansion inside a body cavity is unreliable in all but the higher speed (at least 1100 ft/sec) +P variants of the chambering.

Being a moderate-powered round on the energy scale, the wide diameter of the .45 ACP bullets produce a decreased tendency to overpenetrate, which reduces the projectile's possibility of passing through the intended target with enough velocity to injure another person. The combination of stopping power and controlled penetration makes the .45 ACP practical for police use, although the resulting loss of magazine capacity and/or the larger size and weight of pistols chambered in this caliber has led more police departments in the USA to adopt sidearms in .40 S&W, and .357 SIG.[5] Many US tactical police units still utilize the .45 pistol round, including the FBI's Hostage Rescue Team.[6][7][8] While high capacity firearms are available in .45 ACP, the greater length and diameter of the .45 ACP means that the grip of the pistol must be longer and wider than the grip of a comparable pistol of a smaller caliber; this increase in grip size can make the pistol difficult to use for shooters with smaller hands.

Today most of the U.S. military uses the 9 mm Parabellum cartridge, but the effectiveness of the .45 ACP cartridge has ensured its continued popularity with large caliber sport shooters. Many US Special forces and police units still use this round in the form of modified 1911A1s and Heckler & Koch's SOCOM MK23s and USP Tacticals.

Because all standard .45 ACP rounds fired from handguns or short barreled "submachine" guns are inherently subsonic, it is one of the most powerful pistol calibers available for use in suppressed weapons since subsonic rounds are quieter than supersonic rounds. The latter inevitably produce a highly compressed shockwave, audible as a loud "crack", literally a small sonic boom, while they travel through the air. Suppressors reduce the audible "report" by slowing and channeling the high speed gas generated by the burning/expanding gunpowder before it exits the muzzle resulting in a muffled "cough". Suppressors of course can't act on a supersonic shockwave generated by the bullet breaking the 1100ft/sec sound barrier as this happens after it exits the barrel.

Load variants

Several manufacturers market preloaded .45 ACP rounds in sizes ranging from 117 to 230 (90 in the case of Le mas RBCD) grains (8 to 15 g), with the most popular commercial load being the standard military loading of a 230-grain (15g) FMJ bullet at around 850ft/s (260m/s). Specialty rounds are available in weights under 100 grains (6.5g) and over 260 grains (16.8g); popular rounds among reloaders and target shooters include 185- and 230-grain (12 and 15g) bullets. Hollow-point rounds intended for maximum effectiveness against live targets are designed to expand upon impact with soft tissue, increasing the size of the permanent cavity left by the bullet as it passes through the target.

Most ammunition manufacturers also market what are termed "+P" loadings in pistol ammunition, including the .45 ACP. This means the cartridge is loaded to a higher maximum pressure level than SAAMI standard, generating higher velocity and more muzzle energy. This is a common practice for updating older cartridges to match the better quality of materials and workmanship in modern firearms.

The terminology is generally given as ".45 ACP +P", and appears on the headstamp. It is important to note that +P cartridges are dimensionally identical to standard-pressure cartridges and will chamber and fire in all firearms designed for the standard-pressure loadings. +P loadings should not be used in firearms not specifically designed for them as they are harder on the gun and may cause damage and injuries. It should also be noted that the use of +P ammunition in otherwise justifiable shootings has proven to be the source of increased legal liability in the United States. For this reason, it is increasingly not recommended for use amongst some firearms experts and attorneys specializing in such cases.


  • 1899/1900 self-loading pistols test: Colt M1900 of .38 caliber entered
  • 1904 Thompson-LaGarde Tests: Caliber of new handgun should be at least .45
  • 1906-1907 handgun trials: Colt enters with .45 ACP design
  • 1910 final tests: Colt design out-performs Savage
  • On March 29, 1911 the Colt design is officially adopted- and with it .45 ACP.


  • .45 Auto
  • 11.43 x 23 mm


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