Someone posted a screen capture of this thing. It's apparently a weapon from some game. I did some searching and found someone had done a full-size paper model of it, by using screen captures and some kind of video editing software to generate a 3D model and printer patterns... it would be useful to know how to do that.
Anyway, I was trying to figure out how you might build a real shotgun that looked like the model. It would be an SBR to start with, of course. A magazine would have to be made, and it would have to be recoil or gas operated.
Unfortunately, I don't think it would be possible to build it. The position of the ejection port is the main problem; it's right over the trigger group, and anything cycling back out of the receiver would bite the hand of the operator.