A cap gun or cap pistol is a toy gun that creates a loud sound akin to a gunshot and a puff of smoke when the trigger is pulled. Cap guns were originally made of cast iron, but after World War II were made of zinc alloy, and most newer models are made of plastic.
Cap guns get their name from the small discs of explosive compounds (roughly 1.4 to 1.6 mm in diameter) that provide the noise and smoke, effectively the same as the separate percussion cap used to replace the flintlock in real firearms, although invariably smaller and made from cheap plastic or paper rather than soft metal. Some were typically arranged in plastic rings of six, seven, or eight. There were also single caps, roll caps (of 50 to 500), and disk caps, all of which were actually extremely small versions of percussion fireworks.