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
Revolver Colt Paterson Revolver, the Walker Colt, the Colt's Dragoon and the Colt Single Action Army pistol of the American Frontier era are all good examples of this system. In double-action (DA), the stroke of the trigger pull generates two actions: Thus, DA means that a cocking action separate from the trigger pull is unnecessary; every trigger pull will result in a complete cycle. This allows uncocked carry, while also allowing draw-and-fire using only the trigger. A longer and harder trigger stroke is the trade-off. However, this drawback can also be viewed as a safety feature, as the gun is safer