I spray liberally with Rem-Oil and rub with 0000 steel wool. I have removed a fair amount of rust from several rifles and shotguns belonging to family and friends without affecting the bluing too much--if at all.
This. Personally I use WD-40 with 0000 steel wool for rust removal; I think the solvent properties are better for the task, but most any light oil will get the job done.
