i've looked over yer mesh, its quite good. here's what ya need to fix
-add a steam pipe thing on the barrel at the back
-the legs you send were a bit weird, the "thigh" wasnt lined up properly on the right, and there was a floating cone-like thing, not needed, so just delete.
-the joint inbetween the lower and upper leg parts (two rectangular peices on each side) have an unnecesary chamfer, its just to save polies, doesnt make a big diff, but just some optimization.
-the front and back of the barrel at the bototm have a strange vertex connection, just make it squares like the rest of the barrel.
-the magazine coming down frmo its gun i'd say give it a bit of a curve (add a cut halfway through it)
-make your own grate teeth!
otherwise great job.
when you get to texturing i have a number of ideas.