Pancor Jackhammer
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The Pancor Corporation Jackhammer is a 12-gauge, blow-forward gas-operated bullpup automatic shotgun designed in 1984 and patented in 1987. Only three working prototypes of the Jackhammer were built. Wikipedia
Action: Gas-operated, revolving cylinder
Designed: 1984
Feed system: 10-shot detachable cylinder
Mass: 7.9 kg (17 lb)
No. built: 3 (2 were destroyed in testing)
Rate of fire: 240 rpm