Cool. You need to do something with the edges (like,t he crevices, where one metal part meets another). There's other stuff that would make it better too.
An easier thing that I think should be done is this: The barrell isn't the right colour. I know in the first big bro image, it looks sort of black (dark grey), but in the second it's the same material as the ammo-loading part. I think this one looks better.
EDIT: Try ...'baking'? an ambient occlusion map that u can layer onto the texture. Let me know if you know how to do this or not 'cause if not, I'll send you the tutorial i used a while back. It's a way of making objects look like they're self-shaddowing in ambient light. (Not sure if my terminology is correct, but I tried
..)