That's pretty impressive.
Shad's AA-12 was good, but why not go back to the old days, in 1972, just when they were making protoypes of it.

All of your models are hardcore polygon rape. Stop adding every little ridge of the grip & stuff.
Extrude, your models could use some work.
Like the animations on the R870 aren't even accurate. The pump slides back, and the ejection slides back halfway!