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 M1900 .32 ACP, etc.), yet fired at similar velocities, giving more power. The .38 ACP was also a much faster cartridge than the .38 Long Colt revolver cartridge in service at the time, which fired a 130 grain bullet at (albeit 130 grains being a heavier bullet). Colt was also experimenting with a .41 caliber cartridge for use in the Model 1900, as reported to the Ordnance Department during testing. Like the .41 Long Colt, this probably used a .400 inch bullet. The poor performance of the .38 Long Colt in combat in the Philippine–American War of 1899–1902 resulted in the