really fun build:
quad barrel, chaos rounds, auto trigger (or any other full auto), ak stock, rubber grip, bullet canister.
alternatively:
mini gat, chaos rounds, double tap, drunken grip, drunken stock, bullet canister, and an autoclicker (or carpal tunnel) (or just use an auto trigger)
chaos rounds are just really fun for some reason
the reason im not posting my good build is because the quad barrel full auto is pretty much the best there is, and gets boring