MBAssociates Gyrojet pistol, carbine and rifle - Fired 12mm or 13mm rocket projectiles. Turned out to be a commercial failure. Unfired rounds (if they can be found), can cost as much as
RIA: Gyrojet Carbine – Forgotten Weapons
Gyrojet - Wikipedia
Gyrojet Rocket Pistol & Carbine from the 1960s in Action -The Firearm Blog