Not bad. I'd suggest making them a bit lighter for better contrast, and to add some color in there somewhere. If you're not a fan of wood on your guns (like me), try adding some polymer grips, stocks, and/or foregrips, which most commonly come in black, olive drab, and desert tan. A pixel or two of another color for fire mode selector diagrams (HK weapons most commonly use nice, distinctive red and sometimes also white, for instance) could also liven them up.
That being said, the shapes and details are quite nice.
