A gas-powered, automatic 12-gauge* bullpup shotgun designed by the Pancor corporation, the Jackhammer is quite an intimidating weapon in the same class as Daewoo's USAS-12. The weapon weighs 4.6Kg unloaded and fires 10 12-gauge* Tungsten Alloy Buckshot rounds from its 10-round drum cassette at a rate of 4 rounds per second on full-automatic, so you could cause a hell of a lot of damage with this bad boy. The gun was also featured in the video game Max Payne.
Thanks to TallRoo for the spelling correction.