The M-44 "Pitbull". An automatic bullpup style shotgun, features a top loading system. What is unique about it is that the shells are loaded in a similar fashion as the FN P90. Has a maximum load of 16 +1 shells. The magazine isnt removable like the P90 mag, instead a small latch is near the back of the gun; this latch opens up and the shells are inserted here. Anther unique function is that the shells dont need to be put in one way or the other, as the loading mechanism will align the shells facing forward, no matter which side the shells face; if a shell was to load backwards, it would simply fall out the bottom harmlessly. The shells are ejected out the bottom of the gun, making it usable by either right or left handed individuals. It also has a built on folding front sight.
Got the idea from a Fear 3 trailer, seeing a shotgun just like this.