Gyrojet

The Gyrojet is a family of firearms developed in the 1960s in the United States by Robert Mainhardt and Art Biehl of MB Associates, named for the way they gyroscopically stabilize their projectiles. Rather than firing inert bullets, Gyrojets launch small rockets called Microjets that produce little recoil and do not need a heavy barrel or chamber to contain combustion pressure, though their velocity on leaving the tube was very low, reaching around 1,250 feet per second only after about 30 feet of flight. Produced from 1962 to 1975, the weapons are now rare items among collectors, with even common models priced above 4,000 dollars and ammunition costing more than 800 dollars per round.