I removed some of the barrel of my old M37 Ithaca over 20 years ago. Made it nice/short for hunting rabbits/grouse in the brush.
A couple years back I was moving stuff in one of the sheds and "found" the barrel piece. I'd just held onto it, cut it, put it in a box and forgotten about it. It rusted. where I'd held onto it.
To prove a point I grabbed some 0000 steel wool and 3n1 oil and went to work. Oil on the steel wool, rub lightly, every now and then wipe off the rusty/oily residue and check the finish. More oil and more light rubbing if needed. I keep hearing 0000 steel wool will damage bluing, just haven't seen it happen, yet.
You can see the rust on the right end of the barrel piece.
After the cleanup.
Something I tried the other day, but do not have enough time after the work to decide if it will be a long term type of "fix" for surface rust on a gun/magazine was to use some Never Dull polish. It wiped the rust right off the "new" magazines I bought a few weeks back.
Typical rust under the soft rubber sleeves on the magazines (CZ75 .40 S&W) as received.
After wiping down with the Never Dull "wads."
Don't have any pictures of rusted guns "repaired" with anything because I've never let one of them rust.
Neither of the above methods will "fix" a rust pit. Get the rust (orange looking particles) out of the pit, sure, but the pit will still be there.