A cap gun is a toy gun

Toy weapon

Toy weapons are toys that mimic real weapons, but are designed to be fun for children to play with and not dangerous.-Types of toy weapons:Some are essentially similar to the real thing, but less powerful. Weapons for cutting and stabbing have dull blades usually in plastic. Weapons formerly made...

 that creates a loud sound simulating a gunshot and a puff of smoke when the trigger is pulled. Cap gun

Gun

A gun is a muzzle or breech-loaded projectile-firing weapon. There are various definitions depending on the nation and branch of service. A "gun" may be distinguished from other firearms in being a crew-served weapon such as a howitzer or mortar, as opposed to a small arm like a rifle or pistol,...

s were originally made of cast iron

Cast iron

Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

, but after World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 were made of zinc alloy, and most newer models are made of plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

.

Cap guns get their name from the small discs of shock-sensitive 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

Percussion cap

The percussion cap, introduced around 1830, was the crucial invention that enabled muzzleloading firearms to fire reliably in any weather.Before this development, firearms used flintlock ignition systems which produced flint-on-steel sparks to ignite a pan of priming powder and thereby fire the...

 primers used in real firearms of the mid to late 1800s, although invariably smaller and made from cheap plastic or paper rather than soft metal.