The Gyrojet was an early attempt at a hand-held, rocket projectile firearm. Manufactured in the 1950s, it fired 13mm (later reduced to 12mm due to U.S. 50-caliber restrictions) self-propelled rocket shells. The gun was not very successful; it was nearly useless at close range as the projectiles hadn't accelerated enough to do much damage, and wasn't very accurate at longer range. The missiles weren't that heavy, so wind at medium range would cause severe drift. Also plagued by manufacturing flaws in the ammunition, resulting in 'corkscrewing' flight paths which made accuracy even worse. Now extremely rare, live Gyrojet rounds are selling for approximately $100 each! Here is a video of a demonstration shooting of the Gyrojet pistol.