28 gauge

[edgarspencer]

The stock and fore end would be gone if it got hot enough from the fire, to have caused the cracks, and even then, it would have had to have been quenched. The case hardening process heats a part to 1625F, and then quenched. Original Parker receivers were not an alloy steel, and much more forgiving in the quenching stage. Repro receivers are most likely (never had a reason to run one through my lab) a chrome moly, or nickel chrome moly alloy. If I were going to do a ccase hardening, I’d only go just above the upper critical temp,1325F, and quench in oil or aqueous treated water.

[Bill Murphy]

I guess the end of this sad story is that the receiver cracked in the case hardening process. Is the "gunsmith" someone who has a good reputation in the case hardening business?

[edgarspencer]

Heat treating is not a ‘One Size Fits All’ process, and requires that you have a pretty good idea about the chemistry of the part.
Regardless, the crack, or cracks are most probably repairable by welding. Filler material is available to match the chemistry of the part. Here again, proper pre, and post weld heat treatment is important. TIG, Micro TIG, and Laser welding are appropriate.