That is a repairable crack!
Before my stroke I welded hundreds of M1 Garand receivers and had no problems. I do re-harden the receivers after the weld. Even after I welded a rear lug on them. TIG weld would work for that.
The only thing you need to avoid is the porosity in the weld so run heavy argon with the weld.
Failure is part of success!
This year will go down in history. For the first time, a civilized nation has full gun registration. Our streets will be safer, our police more efficient, and the world will follow our lead into the future!" -Adolf Hitler,1935"