Some one with a lathe should offer to fix it for you. If you were closer I would fix it for you.
Cheapest solution. I've fixed hundreds of threads with thread files that aren't in critical locations.
For a pin and weld, this is it.
Steve Epple at Murray State's gunsmithing school should be able to fix it. He restored threads on a 1911 for us in a summer class.
We have thread files and a lathe at my work. If you were closer I’d see what I could do as far as cleanup goes. Since your doing a pin and weld it might be easier to cut the bad threads off if it’ll leave you enough to thread on.
If you can spin a muzzle device all the way on there it shouldn’t be a problem. As long as you have a half inch of good thread, it’s not going to lose any strength. I would agree that a small triangle needle file or thread file will get you where you need to be well enough to get a new device on. We pin and weld hundreds of devices a year and I’ve seen them looking way worse than that able to be saved with no problem.
So I ended up buy some very fine files and spent a couple days cleaning up the threads and ended up getting it good enough to work a muzzle brake on and off .. not bad for 8$ worth of files
