Finished that luger, just need new grips now.
As for how I did it?
Its pretty simple, the gun was stripped with Steel wool and paint thinner, then I used Birchwood Casey 'Aluminum Black',
You basically drip some onto a rag, and rub it onto the area you want to darken. I used a little bit and spread it into the fabric to apply it lightly, and kind of rub in the inconsistancy so to speak, gives it a nice, old oiled look. After it settles into the metal, a nice polishing works really nice.