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 Action Army, serial number 1, thought lost for many years after its production, was found in a barn in Nashua, New Hampshire in the early 1900s. It was chambered in .45 Colt, a centerfire design containing charges of up to of fine-grained black powder and a blunt roundnosed bullet. Relative to period cartridges and most later handgun rounds, it was quite powerful in its full loading. The Colt Single Action Army revolver, along with the 1870 and 1875 Smith & Wesson Model 3 "Schofield" revolver, replaced the Colt 1860 Army Percussion revolver. The Colt quickly gained favor over the S&W