Colt Walker of Texas had been the major purchaser of the early Paterson Holster Pistol (No. 5 model), a five shot cal .36 revolver, and Samuel Walker became familiar with it during his service as a Texas Ranger. In 1847, Walker was engaged in the Mexican-American War as a captain in the United States Mounted Rifles. He approached Colt, requesting a large revolver to replace the single-shot Aston Johnson holster pistols then in use. The desired .44-.45 caliber revolver would be carried in saddle mounted holsters and would be large enough to dispatch horses as well as enemy soldiers. The Colt Walker
Colt Single Action Army the .44 American was the cartridge used in the 1,000 Smith & Wesson Model 3 revolvers issued to the troops. After the tests, the Colt was declared the superior revolver and the government specified that a .45 caliber cartridge would be required. With the adoption of the Colt Single Action Army revolver in 1873, the service cartridges were Copper-cased .45 centerfire Benét inside primed "Colt's Revolver Cartridges" loaded with 30 grains of black powder and an inside lubricated bullet of 250 grain. They were manufactured at Frankford Arsenal, Philadelphia, PA, through 1874. In 1875, the cartridge was shortened so that