I've noticed a few things you made in your work.
Too many colors.
No AA anywhere.
You used one same 0,0,x colors at all times. (x being the change of value from the gun)
It's a really good piece, but metal isn't full-out grey.
Use less colors and like Bram said, use a different color inside the piece.

It isn't a bad piece, though, I like it. =]