The Plum Brown for muzzleloaders works good, with boiling, and fine wire brushing between coats. The boiling turns the brown oxide to the black. Available most everywhere.
It is the best I have ever used. Some solutions give a slightly different color, some running to more of a blue while the gun goddess is more of a matte black.
Sorry. I guess I could have told you it was also called Gun Godess. I just looked at the name on the top of the bottle and it says Olde English Rust Bluer.
It really is good stuff. I have only used it once, but got excellent results and its tough. I have tried to steel wool it off with fine steel wool and it just doesn't come off.
Beautiful soft black finish if you do it right.
I have also tried the Mark Lee Express Blue. It also worked very well but the instructions are different. I don't think it takes as much of a bite in the steel.
I need to get a bottle and play around with some small parts. I need to make a long pan to boil a barrel action in.
How are you guys keeping the bore sealed? Seems I read to wipe the bore with some spar varnish. Then use some paint striper when done. Or is that even necessary?
A threaded rod down the bore with some rubber plugs and nuts??
I don't do anything special(other than initial de-greasing) with the bore. After boiling, the bore is immediately dry from the heat. After I finish carding, I run a clean patch down the barrel using a de-greased rod.
I've rust blued maybe a dozen rifles so just consider the source.