I recently picked up 4 AK receivers that are “raw”. They have light surface rust in some spots, so I would like to put a finish on them ASAP. Does anyone have any recommendations? I was thinking about heating them and then dipping them in motor oil to get that black finish. However I don’t know if heating them over a propane flame will mess up any tolerances or if that finish is durable. Any help is appreciated.

Propane heat should be fine, you shouldn't keep it on there long enough to get it red hot. Depending on the receiver it may just be the pin holes and ejector that are hardened and not the whole thing. As for finish you could do oil, or black oxide pretty cheap until you get ready to do the final finish