28 gauge

[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.