First and foremost, let me say it has been a pleasure discussing this Mauser HSc with you. Second, please keep in mind that I am never wrong! Just kidding Peter. I try to keep an open mind cause with most things it life, they are not always as the appear.
If the HSc is matching, the facts remain the same and that is that the slide is plum color and the frame is a nice high polish blue.
I have no idea if high heat would turn a hot salt blued slide a plum color and do it that evenly? I guess anything is possible. However with Luger's & P38's which is what I mainly collect, the plum color is associated with the temperature of the holt bluing salts.
Possibly ROID will respond in the near future regarding his postings.