percussion cap

American  

noun

1. a small metallic cap or cup containing fulminating powder, formerly exploded by percussion to fire the charge of small arms.

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percussion cap British  

noun

1. a detonator consisting of a paper or thin metal cap containing material that explodes when struck and formerly used in certain firearms

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Etymology

Origin of percussion cap

First recorded in 1815–25

Example Sentences

One of the revolver’s chambers was empty, and officers found an expended percussion cap.

From Los Angeles Times • Jan. 29, 2022

The percussion cap had detonated, but the gunpowder failed to ignite. 

From Slate • Jan. 31, 2014

Reason: the bomb's firing pin had tripped, but the percussion cap was a dud.

From Time Magazine Archive

Remove the priming load or percussion cap and lock the cased rifle in your vehicle or storage shed.

From Time Magazine Archive

Either the copper percussion cap might fail to spark, or the black powder in the barrel might fail to ignite because of dampness.

From "Chasing Lincoln's Killer" by James L. Swanson