Good job! I love modelling weapons, it massages my OCD of having to snap every vertex to another vertex so everything is tidy and symmetrical. Lovin' the chunkyness of it too, the front-end looks like it'll be pumping out some HUGE rounds. Keep it up!
I think it realy looks good only little crit would be the pistol grip looks a little to curved. Trying to remember was the large barrel a 20mm grenade launcher. How is the low poly model looking like..........dave