Colt Peacemaker of 1873

Mason, William. Improvement in Revolving Fire-arms. US Patent 158,957. January 19, 1875; Busk, Hans. The Rifleman’s Manual; or Rifles, and How to Use Them. Second Edition. (London: Charles Noble, 1858), 34; Haven, Charles T. and Belden, Frank A. A history of the Colt revolver: and other arms made by Colt’s patent firearms and manufacturing company from 1836 to 1940. (New York: William Morrow and Company, 1940), 145 - 149.
Colt Safety and Instruction Manual. (Hartford: Colt Manufacturing Company, 1993), 19.