all good suggestions above, when we get old ,froze up ones, we simply soak them in kerosene for a few days, ( remove the grips obviously) then use the penny trick or the edge of the copper pipe on any "pits" but simple rust we use Choreboy, brass or bronze wool and some rust type oil and work the areas needed, then oil it down good. the non metallic wools ,will not hurt any of whatever bluing may be left on the gun...........
deep pitting then you have to address them differently, draw filing, polishing, buffing etc to remove the pits, and blend in the surrounding area....cold blues are ONLY temporary, needs to be hot blued, to do the job properly.......... :wink: