Because sometimes, you have to throw stupid at the wall and see what sticks.

Russian KS-23 shotgun on the China Lake animations? 23mm shotgun is a big bad boomstick, and if they'd fit, the anims would give it quite the powerful feel. Plus the low rate of fire and slow reload would help balance the power a bit. Bonus points for Dozer-fighting AP slugs.

I bet there's a model from CoD: Black Ops someone's probably ripped, there's a chopped down model on Gamebanana, and if someone's really desperate to wade through Source model/texture files I think I still have the stuff from Firearms: Source, plus various Garry's Mod and Left 4 Dead 2 addons.