Rust bluing will take a little time, but will produce a very durable finish. I use Pilkington's Classic Rust Bluing from Brownells, here is the link
http://www.brownells.com/aspx/NS/st...5&title=PILKINGTON+CLASSIC+AMERICAN+RUST+BLUE
Basically the steps are as follows.
1. Polish the parts (I hand sand with a block to keep the flat places flat, starting with 180 grit and progressing to 400 grit. What grit you start with depends on the condition of the gun. It is not necessary to go beyond 400 grit.)
2. Degrease the parts completely, any grease, oil or fingerprints will show.
3. Apply the bluing with a cotton ball (after degreasing, the parts must be handled with rubber gloves to keep them free from skin oil)
4. let the parts rust for about three hours. ( on the first coat, you reapply the bluing after about an hour).
5. boil the parts in plain water (distilled is best) for about 10-20 minutes. This turns the red rust to black rust.
6. remove the parts, dry them with air. steel wool the parts with 0000 steel wool (steel wool must be degreased)
7. reapply the bluing (just enough to barely dampen the surface, it should dry immediately)
8. wait 3 hrs, boil, steel wool.
9. repeat for a total of 4 to 10 times depending on how it looks.
10. let it sit for 24 hrs before oiling.
The bluing comes with instructions which should be followed exactly. After the first coat, it will not appear to rust much, at that point you are deepening and evening the finish.
I have done about 6 guns with rust bluing, and I seem to do a better job with each one. You may want to try just a piece of steel first to get the hang of iit. I usually would do one round of bluing a night due to time constraints, and after I used the steel wool, I would let it sit until the next night.
Jim