A multiple-shot shotgun bolted onto an assault rifle.
 
INEEL researchers redesigned a conventional 12-gauge pump shotgun to make it work differently.

Researchers at the Idaho National Engineering and Environmental Laboratory (INEEL) were approached by a federal law enforcement agency to create a better firearm for forced entries. The traditional method requires firing a shotgun at a door's hinges or lock and then switching to an assault rifle for confronting the bad guys. The answer: A multiple-shot shotgun bolted onto an assault rifle.

INEEL researchers redesigned a conventional 12-gauge pump shotgun to make it work differently. Standard shotguns cycle cartridges by moving the bolt to the rear. The new design holds the bolt stationary and moves the receiver and barrel forward, letting the receiver be shorter and the barrel longer. The Idaho Integrated Breaching shotgun carries a replaceable box magazine to rapidly reload and select alternate munitions, such as less-than-lethal rounds. The new firearm was developed in a rapid four months and with little cost.