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 Open Top Pocket Model Revolver White patent for metallic cartridges firearms manufacture expired (c. 1870) the Colt's Patent Fire Arms Manufacturing Company started working on its own metallic cartridge revolvers (Colt had previously been manufacturing the so-called Richards-Mason conversions). Thus, Colt introduced its first rear-loaders in 1871: the Colt House/Cloverleaf and the Colt Open Top Pocket Model Revolver. In the 1870s the firearms market was awash with cheaply made knockoffs of the .22 caliber Smith & Wesson Model One which sold for about $2. Colt's president Richard Jarvis decided it would not compete directly with the knockoffs; that its .22 would be of Colt quality.