PERCUSSION CAP • DICTIONARY ONE.COM • Definition of Percussion cap

... enemy's breastworks, leaning against a tree, resting on his left knee, his loaded rifle across the other. In his right hand, between his forefinger and thumb, in the act of being placed upon the nipple of the gun, was a percussion cap. His frame was rigid, cold, and stiff, while his glossy eyes seemed to be peering in the front as looking for a lurking foe. He was stone dead, a bullet having pierced his heart, not leaving the least sign of the twitching of a muscle to tell of the shock he had received. ...

— History of Kershaw's Brigade • D. Augustus Dickert

... they talk, in dust, or mud, or snow, Both bored to death, and both afraid to go! Your hat once lifted, do not hang your fire, Nor, like slow Ajax, fighting still, retire; When your old castor on your crown you clap, Go off; you've mounted your percussion cap. ...

— The Poetical Works of Oliver Wendell Holmes, Complete • Oliver Wendell Holmes, Sr.