Percussion cap

A small metal cup containing impact-sensitive priming compound that a firearm hammer strikes to ignite the powder charge. It replaced the flintlock’s exposed priming pan with a compact, weather-resistant ignition system.

Percussion lock: A firearm ignition mechanism in which a hammer strikes a percussion cap to ignite the main charge. It holds and strikes the cap, directing its flash into the firearm’s breech.
Flintlock: A firearm ignition system that uses a flint striking steel to shower sparks into a priming pan. The percussion cap replaced its exposed spark-and-pan ignition method.
Muzzleloader: A firearm loaded through the open end of its barrel rather than from a breech-loading cartridge. Percussion caps commonly ignite the powder charges of muzzle-loading firearms.
Waterproofing: The prevention of water from entering or damaging an object or system. Enclosing priming compound in a cap made ignition less vulnerable to damp than an open pan.
Nipple (firearms): A small projection on a muzzle-loading firearm that holds a percussion cap and channels its flame into the barrel. The cap sits on the nipple, whose passage carries ignition to the powder.
Alexander John Forsyth: A Scottish clergyman and inventor who developed an early chemical ignition system for firearms in the early nineteenth century. His fulminate-based ignition work helped establish the principle behind percussion ignition.
Percussion revolver: A revolver whose separate powder-and-ball chambers are ignited by percussion caps fitted over rear nipples. Each chamber uses its own cap to fire the loaded cylinder.
Breechloader: A firearm loaded through a breech at the rear of the barrel. Cap ignition helped bridge muzzle-loading firearms and later breech-loading systems.
Mercury(II) fulminate: A highly sensitive explosive compound historically used as an initiator in percussion caps and detonators. It was a common priming compound whose impact sensitivity made the cap work.
Joshua Shaw: An English-born American inventor associated with developing and patenting a practical copper percussion cap in the 1820s. His cap design helped make percussion ignition practical for firearms.

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