Rust bluing doesn't turn color like that and was almost unheard of in the US in the 1970s.
Almost certainly rust blued originally, and should be redone. I'd be more afraid of wheel buffing that was part and parcel to hot bluing in the 70s?
Where's the pics?

Range testing Low Wall 17HMR on a rare Feb. lull in the Livingston windstorm..Rust blued brl, charcoal blued action and hot blued scope.