A while back I got a number of rusty AK mags at a gun show. What I did was:
scrub off surface rust with steel wool and oil
wash off and degrease with hot water and dishwashing liquid, rinse with hot water then rubbing alcohol
apply naval jelly rust remover to the rust remaining in the deep pitted places, leave overnight, rinse with boiling water then rubbing alcohol again to dry and degrease
refinish with two coats of matte black BBQ grill paint and bake in oven one hour at 400 degrees
They were all mechanically sound before, and all worked fine before, but I did not want the rust to spread. And I like the nonreflective matte black look.