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The firearm involved in the incident was a .44-caliber cap and ball revolver, a black powder gun that uses a lead ball and percussion caps.—Caleb Lunetta, San Diego Union-Tribune, 12 Feb. 2026 One of the revolver’s chambers was empty, and officers found an expended percussion cap.—Los Angeles Times, 28 Jan. 2022 Oxygen generators use a chemical reaction initiated by a percussion cap.—John Cox, USA TODAY, 4 Dec. 2020