Rust blueing,
4 tablespoons salt
8 ounces peroxide
8 ounces white vineger
Mix warm so the salt will blend, degrease the barrel with something.. Rubbing alchehol is what I used. Dampen a paper towel in the solution and apply in long single strokes. It will rust, when it gets an even fine coat of rust put it into a pan (trough) of boiling distilled or rain water. It will turn black. Rub the excess black off with a paper towel and repeat. 6 or 7 times till it won't rust much anymore. Worked for me, and cost me nothing but time. Don't touch the metal with your fingers you don't want the oil getting on the gun during the process.
I linseed oiled the barrel to seal it after it blued the way I wanted, it really does get a deep black-blue. Also on the final rub down before the linseed oil I used 4X steel wool instead of the paper towel.