Hi Mike,
Well I'm not any sort of expert on this (at least not yet), but I did a lot of experimenting working on this project. The best results I achieved was to use Birchwood Casey Super Blue. I applied it on the metal with some of those cotton balls on a wire stick made just for this type of thing and followed the instructions. One thing I found out was if I carded it back with 0000 steel wool before the bluing was totally dry on the metal you would get more of a white. I tried pitting the metal with bleach and that worked fairly well. On the lock plate and screws etc. that already had a finish, I used Naval Jelly to take it off. Works fairly fast. Then would blue again if needed. This was the method I used, and it is not the only method. I corresponded with a gun builder on another forum who had just completed a North Carolina Mountain Rifle (a beautiful piece!). He also put a gray finish on the metal by using Super Blue. However, he applied the bluing then let is sit overnight before carding. The bluing will rust and lightly pit the metal as it sits. He then used a scotch brite pad to card off the bluing to get his gray. Looks fantastic! Where I dismantled everything from my gun while working on the finish, he left the furniture on. This allowed some of the almost black bluing to remain in the nooks and corners of the rifle. Gave it a more authenic antiquing appearance.
Anyway, some thoughts. Good luck with your project.
Scott