Take the brown colors from the pick up view and replace all the pixels in the pump and stock one color at a time till you get it from black to brown. Try using a darker brown for dark spots and lighter for the grey area's. thats what i do i know it seems like the hard way, but it usaly looks alot better after. As i found MOST, not all, but most paint programs, have issues turning black into a color. And if this is supost to be a pump shotgun, ur pump animations may need tweeking, as that grey ring in the front is supost to be the pump stop and should be resting against it, and not visable at all.
Damn Benelli has simalr shotgun styles. this is a m4 super

sorry about that, they all look alike lol still for the pump action, make the pump u have the edited and moved closer to that ring, and little bit of the tube before the section of the gun. Then take the pump and move it down the tube for about 3-4 frames. cuz i think your trying for this style but it dont quite fit with this gun set up.

i know this on is chrome and black and your looking for wood and black metal, but its the wingmaster style i think your after.