45 ACP

During the 1890s the world’s militaries were in an increasingly fast-paced race to develop and field the latest technological advancements. In 1892 the U.S. Military unilaterally adopted the Colt double action revolver and 38 Long Colt cartridge. This change was especially resented by members of the cavalry and artillery, who had been fielding .45 caliber revolvers since 1847. By 1900, when many militaries began considering the automatic pistol, there was a divide within the U.S. Ordnance Department, with many calling for a return to the .45. The search for an automatic pistol would largely take place with Colt, using designs from John Browning. What began with the Model 1900 and the 38 ACP, eventually evolved into the Model 1911 and the 45 ACP. This journey was not without controversy, and requires some explanation.

Selecting the .45

The history of the 45 ACP begins in late 1903, when Col. John T. Thompson notified Colt’s that the U.S. Ordnance Department would be moving to require all future pistol cartridges to be of no less than .45 caliber.

That decision came at the recommendation of a board organized to test what type of bullet “will have the shock effect and stopping power at short range necessary for a military pistol or revolver”. The Board consisted of Col. Thompson, officer in the Ordnance Dept., and Maj. Louis LeGarde, U.S. Army surgeon. Simply put, testing was largely a formality to provide scientific data telling the military what it wanted to hear. Despite announcing their conclusion less than half way through experiments and a clear bias throughout testing, the study was considered authoritative.

Men like LeGarde knew from experience that wounds from bullets having a low sectional density were more severe than those from bullets of a higher sectional density when traveling at the same velocity. Sectional density and velocity being equal, as was the case with nearly every pistol cartridge produced up to that point, larger bullets have more energy and make bigger holes. The problem was twofold; they didn’t have the scientific data to understand or explain this phenomenon, and most official testing derived its conclusions by observing bullet penetration.

Tests by Thompson and LeGarde were conducted between November 1903 and March 1904. Cartridges used included 30 Luger, 9mm Luger, 38 Colt, 38 ACP, 45 Colt, .455 Webley, and .475 Eley. Testing observed and recorded that “as a rule, to which there were no exceptions, when an animal was hit in a vital part … the shock effects were immediate or nearly so in all cases.” And also that soldiers armed with the pistol should be trained in basic human anatomy and “drilled unremittingly on the accuracy of fire” due to “the large amount of target area of the human body which offers no hope of stopping an adversary by shock or any other immediate results when hit”. Indifferent to this, and the known fact that the 1899 Hague convention prohibited their use, the two men were most impressed by the results of soft lead hollow-point bullets, which were only tested in the 45 Colt and 455 Webley. They concluded and recommended that nothing less than .45 caliber be adopted in the future.

Progress with Colt and UMC

Available documents suggest that after being informed of the caliber requirement by Thompson, Colt turned to the Union Metallic Cartridge Company. In February 1904, William Thomas, head of UMC’s Ballistic Laboratory, furnished specifications to set up tooling for the proposed cartridge. It is unknown if Browning created the initial cartridge, or if the credit more rightly belongs to Thomas. Regardless of its exact origins, Browning was deeply involved in every detail of the cartridge’s development, and the first large batch of samples was shipped from UMC in March 1905.

In March 1904 the Frankford Arsenal was ordered to “start development of an effective automatic pistol cartridge”. Available records indicate that intermittent testing was done throughout 1904 and 1905 with a commercial cartridge produced by Winchester for the Colt automatic pistol. That cartridges were available from Winchester in 1904, lends merit to the theory that Browning had followed his typical habit of sending cartridge prototypes to Winchester’s ammunition department for production samples to be made prior to UMC’s involvement. Pistols were sent from Colt to Frankford Arsenal during 1905 for testing of their cartridges.

During March and April of 1905 samples were sent between Colt, Browning, and UMC for a rimless .45 caliber cartridge with the same case and overall length as the 38 ACP, using a jacketed .452″ 200gr bullet and 5.5gr Bullseye powder, cannelure on the case with no crimp at the case mouth. After reducing the powder charge to 5.1gr, for a velocity around 900fps, the samples were approved and 1 million were ordered for testing with Colt.

By December 1905 Colt released it’s new .45 Automatic Pistol, and both UMC and Winchester had begun full-scale production of its 200gr ammunition.

Between 1905 and 1908 Frankford Arsenal continued experimenting. Both rimless and semi-rimmed cartridges were developed, but by 1906 they had at least settled on a rimless cartridge and a 230gr bullet with a velocity of 800fps. When Frankford was required to produce ammunition for pistol trials in 1907, they proved incapable of producing reliable cartridges or the desired quantity. Contracts were given to UMC for production using their standard commercial case with the increased 230gr bullet and specified velocity of 800fps. During testing from 1907 to 1911 Frankford Arsenal continued to attempt production of cartridges with inconsistent case lengths, while nearly all ammunition for testing was provided under contract with UMC or Winchester.

Military Adoption

Throughout pistol trials minor changes were also made to the rim, extractor groove, and primer of the cartridge. By 1909 the design had largely been standardized on the UMC case with 230gr bullet. The Colt pistol was adopted by the U.S. Military on March 29, 1911. The cartridge was officially adopted shortly thereafter as the Cal. .45 Automatic Pistol Ball Cartridge, Model of 1911. It specified a slightly tapered 230gr fully jacketed bullet, .450-.451 inch in diameter with a velocity of 800fps. The new cartridge would be produced by Frankford Arsenal. Two powders were approved, DuPont Pistol Powder No.2, which was Bullseye powder, and Pistol Powder No.3.

Between 1912 and 1914 an increasing number of companies were contracted to produce the military ammunition. Commercial production of 200gr cartridges appears to have been put on hold at some point to meet military contracts, and was either never restarted or phased out during industry standardization in the 1920s.

In 1917 the Colt New Service revolver was modified to accept 45 ACP with half-moon clips, and the cartridge was crimped at the case mouth to prevent bullets moving forward under recoil.

In 1925 the cartridge was updated again, no longer using a tapered bullet and specifying a .350″-.3515″ diameter. This was increased again in 1932 to .3505″-.3515″.

In the late 1930s DuPont Pistol Powder No.5 was created to more fully fill cases during production and made standard until discontinued in 1940. After 1940 it is unclear what powder was used, the most commonly cited is a return to Bullseye.