I just thought of an excellent idea, though it may be challenging: the M26 MASS. It's a rather small magazine shotgun easily mistaken for a carbine. The most unique feature has to be the most challenging, though. It is pump action, but the pump is on the left side of the barrel, and protrudes outwards as a complex cylinder. The shotgun has an extremely wide spread, making it ideal for CQC. It may require a bit of unorthodox animating in third person, but it'll certainly be worth it. Because there are no versions of this gun on the workshop, Battlefield 4 would be the best place for model/sound sources.

@Torfm I'll try.

Can you make a black variant of this?