I used the "dry brush" technique, Chris. I watched this video on Youtube, but scaled it back quite a bit to make it more subtle, as he went a bit heavy for my particular liking. I used silver paint, and mixed a tiny amount of black in with it, and used a slightly larger brush. You can experiment a bit, and if worse comes to worse, hit the areas with the black spray paint again.
For the scope, you can purchase the Testors or Humbrol brass color, and use the same method. Just don't go too heavy on any of the weathering.