Guys: I saw a couple of "ideas" here that are complete suicide.
Scotch Brite pads of any type with abrasive will remove blueing just about as fast as sandpaper, even with oil.
Never use regular Steel Wool on Stainless Steel!!! Only use "Stainless Steel wool, or a fine Stainless Steel wire brush. Regular Steel Wool WILL contaminate the surface of the stainless with low carbon steel particals which will rust in hours. Believe me, It WILL rust. I'm not speculating here! IT WILL RUST! You can ask any competent weldor about wire brushing a stainless weld with a steel brush. It will rust in a matter of days.
After stainless parts are worked with steel tools , they must be passivated by soaking them in a Nitric Acid solution. The Acid eats all of the ferrous component from the surface of the material leaving only the nickle and chromium exposed to the outside. Nickle and Chromium do not rust hence stainless steel.
Stainless guns are made from 400 series stainless steel. 400 series stainless is ferrous IE magnetic, and will rust on its own, it is kind of rust resistant. Guns can't really be made from 300 series stainless because it is too ductile, and where as it won't readily rust, if it is contaminated with locarbon steel like from steel wool or a wire brush, it will. Those pretty Bass Boat propellers you've seen are made from 300 series Stainless and are then "electro polished" which is passivation with electricity added. Note how shiney they are? They will hardly rust in salt water, they will, it just takes along time, because there is no ferrous steel exposed on the surface.
If you have light rust on a blued surface, the standard method of removing it is to use 000, or 0000 steel wool and some oil. The steel wool removes the rust and the oil seals the metal so it doesn't just rerust. It does not harm the blueing which is nothing more than blue colored rust. In fact steel wooling or carding with a fine wire brush is part of the process called Rust Blueing.
I hope this helps, and you need to test ANY process on a hidden area before trying it on an expensive gun, for that matter on a cheap gun too.
Randy