Anything w/ a very weak acid in it will strip bluing.
Vinegar (acidic acid) works well.
'Naval Jelly' has phosphoric acid in it to do the job and it won't go further than removing the blue. It leaves the steel a gray somewhat motteled color but it cleans right up with scotchbrite or even steel wool.
Most of the commercial bluing removers use phosphoric acid.
Even common Cola soft drinks have the phosphoric acid in them and that's why they will ruin a blued surface if spilled on it. You can use it to that advantage if you really want to, just as you can use ketchup with it's acidic acid content.
I've used Hydrochloric acid (muriadic acid) a very weak soln of about 2 tbs per gallon of water at room temp to strip blueing for years.
It'll remove hot salt blue in about 5 to 15 minutes. Rust blue takes longer. I also use it to remove heat scale from parts but they sit in it for several hours.
The weak soln allows it to work w/o pitting the steel.,,just don't forget about the parts in there over the weekend..
Don't try it with stronger solutions or by heating it or the parts. You'll have nothing but a pitted mess of gun parts on your hands.
Lately I have been using Evapo-Rust. I really like this stuff.
It's not an acid and is entirely safe to use.
If you're going to buy any product to do rust removal,,I'd recommend this stuff over anything else.
Evapo-Rust rust remover description page
Never any worry that the steel under the rust will be attacked by the rust remover chemical. Bluing is a form of rust after all.
I bought it at Home Depot, but many places do not seem to carry it.
My .02
remove bluing
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