Naval Jelly is good for a lot of applications. It will remove the rust...and the blue. And it will leave a phosphate coating that you probably don't want on your gun.
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I used to use Naval Jelly a lot, refurbishing old farm equipment. @Old School is correct though, don't put it on anything you don't want to have stripped to the metal. I've used some phosphating finishes on some trailers, and I like the way the work for what they do
Using ANY acid based cleaner will definitely strip off all traces of bluing. If you want to strip the bluing off of a gun to reblue it, just use plain ole white vinegar. It is gentle and works like a charm.
Post up before and after photos of your results with the Big 45 G gh1950 . I think others will want to see how well these work.