sounds like you have no finish left of these parts that are rusting. If that's the case you need to get it reparkerized(that was the original finish).
I just got through de-rusting 5 Korean Imports that were rusted beyond belief.
I blasted them, degrased and into the park tanks. Parkerizing is a phosphate finish, I use manganese phosphate as it comes out a black color that was like the original GI finish
Small Arms Restoration, Inc.
" I started with nothing and Still have most of it left thanx to the federal gov't