percussion cap
Quick Summary
A percussion cap is a firearm ignition device that utilizes the explosive properties of chemicals like potassium chlorate and fulminate of mercury. These compounds detonate when struck by a small, sharp blow. The concept of detonating fulminates was explored in the late 17th and 18th centuries, but it was Alexander John Forsyth who successfully combined priming powders with firearm ignition in 1805.1
By 1830, percussion caps, credited to Joshua Shaw around 1815, became the standard for igniting firearm charges. These caps, typically made of copper, contained fulminate of mercury and were placed on a steel nipple at the weapon's breech. The hammer striking the cap would ignite the powder charge. This system was easily adapted to existing flintlock firearms. Later, cartridges evolved to incorporate the primer, including those with a percussion cap at the base, leading to center-fire and rimfire ammunition.12
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