Hi Sake,
I understand about adding edge definition with the knife tools (and the ever useful Bandsaw tool) but I think what puzzles me is the superbly clean lines you're getting. I never seem to get clean surfaces/edges like you have there.
Presumably you're having to add knife lines in across the whole model in order to create indents etc. in certain sections? And are you cleaning up the geometry too, so that you can reduce the poly count?
Sorry... lots of questions...
I think what would really help, when you have time... (and if you're inclined of course) is a small tutorial on one of the sections of the rifle... something showing those indents.
Keep up the great work... can't wait to see it finished and textured!
Cheers,
Darren.