Any case hardening method by molten salt bath or not will give a hard case only a few thou. thick. It will do nothing for the yield strength of the action. The only benefit will be wear protection.
FWIW, modern alloy steel actions are usually around 38-42 RC all over. There is no direct correlation to case hardened actions as the hardness testing method is different for the thin case versus a through hardened steel surface.
RAN
