During the late 19th century and early 20th century, the U.S. Cavalry began trials to replace their sidearm arsenal of issued .45 Colt Single Action Army (SAA) in favor of the more modern and versatile double-action revolver in .45 Colt.
After the example of the Cavalry, the Army in turn had fielded versions of double-action revolvers in .38 Long Colt. It was eventually evaluated that the .38-caliber round was significantly less effective in overall stopping-power than the .45 Colt against determined opponents in cases such as the Moro juramentado warriors, who were encountered in the Moro Rebellion.[3][4][5][6] The then-current issue rifle, the .30-40 Krag, had also failed to stop Moro warriors effectively;[7] the British had similar lack-of-stopping-power issues switching to the .303 British, which resulted in the development of the dum-dum bullet in an attempt to compensate for the round's deficiencies. This experience, and the Thompson–LaGarde Tests of 1904, led the Army and the Cavalry to decide a minimum of .45 caliber was required in a new handgun. Thompson and Major Louis Anatole La Garde of the Medical Corps arranged tests on cadavers and animal remains in the Chicago stockyards, resulting in the finding that .45 was the most effective pistol cartridge. They noted, however, training was critical to make sure a soldier could score a hit in a vulnerable part of the body.
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 an enlarged version of the prototype .41 round. The result from Colt was the Model 1905 and the new .45 ACP cartridge. 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 (14.9 g) bullet fired at a nominal velocity of 850 ft/s (260 m/s). The resulting .45-caliber cartridge, named the .45 ACP, was similar in performance to the .45 Schofield cartridge, is only slightly less powerful and significantly shorter than the .45 Colt cartridge that the United States Cavalry was using at the time.
By 1906, bids from six makers were submitted, among them Browning's design, submitted by Colt. Only DWM, Savage, and Colt made the first cut. DWM, which submitted two Parabellums chambered in .45 ACP, withdrew from testing after the first round of tests, for unspecified reasons.[8]
In the second round of evaluations in 1910, the Colt design passed the extensive testing with no failures, while the Savage design suffered 37 stoppages or parts failures.[8] The Colt pistol was adopted as the Model 1911.
The cartridge/pistol combination was quite successful but not satisfactory for U.S. military purposes. Over time, a series of improved designs were offered, culminating in the adoption in 1911 of the "Cal. .45 Automatic Pistol Ball Cartridge, Model of 1911", a 1.273 in (32.3 mm) long round with a bullet weight of 230 grains (15 g). The first production, at Frankford Arsenal, was marked "F A 8 11", for the August 1911 date.
Other US military cartridges include: tracer M26 (red tip), blank M1921 (rolled crimp, red paper wad), M12 and M15 shot shells, and M9 dummy (holes in case).
The cartridge was designed by John Browning for Colt, but the most influential person in selecting the cartridge was Army Ordnance member Gen. John T. Thompson. After the poor performance of the Army's .38 Long Colt pistols evidenced during the Philippine–American War (1899–1902), Thompson insisted on a more capable pistol cartridge.[9]
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