This looks great already :) Very modular. Also like the grid. Are you doing anything for the foreground? Right now it just cuts off. Or is that now in view?
You could put the accessories (optic, bipod, sling) on their own texture sheets if they're genuinely modular pieces that could be re-used on other weapons.
For an example of a modular character design, check out Jesse Sosa's excellent example http://oldwiki.polycount.com/SkankerzeroModularCharacterSystem (the images aren't up on the new wiki yet)
Thanks for the replies, everyone. Modular seems like the way forward - back to work for me. Time for a pot of coffee and some Boards of Canada, I think....