So yeah, this is a mac 10 i am still working on, trying to get better at texturing. a few things:

The Stock is missing on purpose, i am having it as a separate piece.

The normals need fixing, as i keep getting errors in max, and help would be so great.

The text sucks on the gun so i will either re-do it, or remove it.

The rear is very messy and needs fixing, as well as some details to be added on the left side of the receiver.

Could you post some wireframes?

Besides the back end (which you're already aware of) I think there are just a few scratches which are oddly placed. The grooves, for example, have sustained the largest scratches while the edges seem untouched. Same around the clip area where you'd figure (well I would, but then again I don't know much about weapons) there would be some damage as well due to mishandled magazine insertion. But then you also don't want to go overboard with scratches and whatnot, so perhaps just rework a few areas on the weapon.

Other than that the model itself looks solid, although it would be better to see some wire frames. Nice work.

renders are pretty dark, looks like you have some shading/normal issues on the back part where the folding stock attaches, also on the grip. Lacks detail basically everywhere, foresight has no sight post ... texture generally looks low-res, scratches are too uniform in colour, scratches in recesses where there should be dirt/grime buildup instead. Also the tubular out-dent at the base of the magwell is incorrectly modelled (pokes out too far, check this ref)

renders are pretty dark, looks like you have some shading/normal issues on the back part where the folding stock attaches, also on the grip

Yeah, i already know that, i did say at the top

Thanks for the other crits though, will definitely work on them.