45 was the most effective pistol cartridge. Thompson and Major Louis Anatole LaGarde of the Medical Corps arranged tests in 1904 on cadavers and animal remains in the Chicago stockyards, resulting in a finding that the. 38 Long Colt pistols during the Philippine Insurrection (1899-1902). Thompson insisted on a real "man stopper" pistol, following the poor showing of the Army's. Thompson, (yes, the same Thompson as in Thompson submachine gun), a member of the Army Ordnance. The cartridge was designed by John Browning of Colt, but the real influence over the choice of cartridge for the new Army pistol was Gen. The very first production, at Frankford Arsenal, was marked "F A 8 11", for the August 1911 date.
Over the next few years 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 inch cartridge with a bullet weight of 230 grains. The cartridge/pistol combination was quite successful but not satisfactory for U.S. Winchester and Colt, working together, developed a response released in 1905 as the ".45 Automatic Colt" matched to a new Colt pistol chambered for the cartridge. In 1904, the Frankford Arsenal and commercial manufacturers were asked by the U.S. 45 ACP Cartridge was conceived in the early days of the 20th Century.