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 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 (15 g) bullet fired at about 850 ft/s (260 m/s). The resulting .45-caliber cartridge, named the .45 ACP, was similar in performance to the .45 Schofield 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 Springfield rifle cartridges in use by the military 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 Luger P08 pistols adapted to the .45 ACP cartridge, withdrew from testing after the first round of tests, for unspecified reasons. 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.
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. The resulting Colt design was adopted as the Model 1911.