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 1851 Navy Revolver sighting arrangement, these revolvers and their modern replicas generally are quite accurate. The first metallic cartridge revolver made by Colt was the Thuer-Conversion Model Revolver, a design that would not require a cylinder with cylindrical chambers so as not to infringe on the Rollin White patent. A small number (about 1000–1500) of Model 1851 Navy revolvers was converted, using front-loaded, slightly tapered cartridges to fit the chambers of the cylinder reamed to a slight taper. After the expiration of the Rollin White patent (April 3, 1869), Colt 1851 (and 1861 Navy) Revolvers were converted or newly made to fire .38