HI. Good question here. I think we have to remember that this weapon, as all weapons in the armed forces, no matter which country we would be talking about, would be well maintained at all times, so there really woldn't be a whole lot of the local ground coloring on it, except for the lower area(s) where the men were walking around it. In offering an off-the- cuff opinion, I would say maybe a real light dry-brush of aluminum or sliver in certain areas where the factory paint job had been worn off to a degree by use and constant cleaning. (And this would depend on just how much 'use' you want to depict on the gun too.) Your washes will give you the shadow's effect so you've already built that in, so to speak.
It's something to consider anyway. Good luck
Take care, sgirty
