"Temper" isn't the correct term there. Temper is what you might do to a hardened piece of steel, to remove some hardness, brittleness, as if to a knife blade. The heat from a torch would introduce some carburization; that is strictly on the surface, probably less than .001. Color case hardening is deeper--I think maybe 3-5 thou. But there are others much more knowledgable than I on this subject; I hope they chime in. But the point is that torching the receiver would be less than skin deep and would have no effect (IMO) on the metallurgy; the steel would be fully normalized after the procedure--the crystal stucture would be unchanged. Color case hardening (to which you would assume the receiver was doubtless subjected) only affects the very outside of the case, that portion where the carbon molocules can attach; the interior remains soft
