TargetTalk

victor high standard with a hex nut holding lower to barrel. while taking apart to clean, hex nut broke in half leaving half inside barrel. I took it to a gunsmith who remove broken bolt, regrooved opening, and inserted a new size hex bolt. this did not hold very long ( few hundred rounds ). the opening in barrel that was regrooved has seemed to have lost its threading and the bolt will not lock tight.
Looking for suggestions on the next step to repair this. I know you can only regrooved this opening so many times before it is too large to be of any use. Try to regroove it again or another method?Any thoughts? Thanks in advance

Heli-Coil or similar thread inserts might work

Yes. A heli coil or a time sert.

if you can't find a heli-coil of the proper threads, a competent machinist can drill the hole oversize, machine a piece of round stock to fit the hole, center-bore it, thread it for the proper screw, and silver-solder or weld it in place