Imagine a pump action shotgun. Good home defense weapon, right? Most of them have a plain wood or synthetic front grip-- where you hold it with your non-dominant hand, and where you pump it to cycle the action. Some of them have a pistol-grip (vertical grip) for the front grip. Some of them have a built-in laser or flashlight on this vertical front grip. NEXT LEVEL: How about mounting a working pistol up there, so the handle of the pistol is also the thing you grab and pump the shotgun with? But the pistol would have its own trigger, that you could squeeze to fire a pistol round regardless of whether or not you also were squeezing the shotgun's trigger. The pistol barrel could be just under the magazine tube. Imagine a pistol action like the Ruger MKI, MKII, MKIII. Fixed barrel and receiver, and no moving slide to complicate things. Just a stubby little bolt that is surrounded by the receiver except where it protrudes out the back when firing. That would be a good design to start with, and enclose in the fore-end grip of a pump shotgun. Just don't block the ejection port. I wonder if the Ruger .22 pistol design could be made larger and modified to work with a centerfire round like 9mm or .357 Sig? P.S. The idea of putting a compact gun underneath a larger long gun is not new. The military has done this for years, with a grenade launcher under the M16. In the civilian world, you can get a kit to mount a pump action shotgun (Short Barreled, or an A.O.W.) under your AR-15 type weapon.