During the mid-19th century and later, were muzzle loading percussion cap rifles frequently used in the frontiers of the American West, or were flintlock weapons still dominating in frontiers? - Quora
NRA Blog | A Brief History of Firearms: The Percussion System
The Flintlock's Replacement: Percussion Cap - How Flintlock Guns Work | HowStuffWorks
Original U.S. Civil War and Indian Wars Percussion Caps in Tins Collec – International Military Antiques