Boy with Pop gun Circa 1950 (Vintage 8mm Home Movie Footage). A popgun is a toy gun that uses air pressure to fire a small tethered projectile (often cork or foam) out of a barrel via piston action. The mechanism consists of a hollow cylindrical barrel which is sealed at one end with the projectile and at the other with a long-handled plunger.The plunger is rapidly forced down the barrel, building up internal air pressure until the projectile is forced out with the "pop" sound that lends the toy its name. The projectile may be tethered to the toy to prevent loss or for safety.