Shooting technical advice
All really effective polishes are likely to remove metal to some degree, as they consist of tiny abrasive particles in either liquid or wax.

You use a very slightly abrasive polish every day when you clean your teeth, but the abrasive element in toothpaste is usually nothing more than relatively soft chalk I would be tempted to try with Brasso or some similar metal polish, and if this doesn’t work then get the gun professionally cleaned by a gunsmith.