[Unclenick]

Rust is a form of oxide. You have a couple of options here. If you can take the gun down and have a long enough container, degrease the tube with a strong solvent and then boil it in distilled water. This may convert the red rust to black magnetite which is what bluing is. However, older rust that has developed pits underneath it won't respond well. It needs to be removed to prevent it from penetrating the steel further. I recommend a product called Evaporust. It is a chelating compound rather than the usual acids and reacts to turn the rust black and loose and it then brushes out. Polish afterward. It will leave the surface slightly matte. Polishes on cloth patches should handle it. Bronze wool or a 100% copper scrubbing pad, like Chore Boy, would be preferable to steel wool. Stainless steel wool may be OK because the particles it leaves behind should resist rusting, but I'd have to try it before I was sold on it.

Regarding steel wool, it can leave traces of iron behind that initiate new rust if you don't get it perfectly cleaned off. That's really the only drawback to it, and careful cleaning will prevent the problem.