I have a bolt gun that I had threaded and a muzzle brake installed a while ago. It is threaded in 1/2x32. I received my harvester suppressor and purchased the 1/2x32 thread insert but it will not thread on. I goes on without resistance for about 1 1/2 rotations then gets so tight I can't twist it by hand anymore. I looked at the muzzle threads and noticed an odd profile. After I researched a bit I'm thinking they are buttress threads.
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So my question is, are these indeed buttress threads? Can I run a die over them to relieve wedge profile so the thread adapter will work ( needs to maintain concentricity for the suppressor)?

I don't really want to have them cut off and retreaded to avoid losing barrel length.

Looks like the gunsmith ( used loosely) did not cut the threads correctly or that the cutter was badly worn. What caliber/brand of gun? All you will do by running a tap over the threads is remove more material and not get the correct depth and pitch. I would find a GOOD smith and let him cut off the old threads and re do the threads. Make sure to confirm that the smith does the work on a lathe and off the centerline of the bbl. and that he re crowns and laps the muzzle correctly. Don't laugh, have had a ton of redo work because someone thought they were a real gunsmith.

Thanks for the response WCT. The rifle is a Winchester 300WSM. I'm a little confused with your thoughts because 1. The muzzle brake he installed threads on nice and tight 2. If it was a poor thread job why would the brake go on smooth but not the thread insert?

Many times I have had stuff come in that someone else has worked on. Muzzle devise screws on, but is loose like AeroE said. Then I try to put another type of muzzle devise on and NO GO! At that point I would check threads with a thread checker (go figure) and see if the threads were done correctly. As for length of bbl hurting accuracy, unless you are shooting high power/ long range matches, and hand loading, it should not make enough difference in impact that you can not adjust for. When I do that job, I get the threads down to the point that the muzzle devise will barely thread onto the bbl (1/2-3/4 of a turn) then I step down to only making .001-.002" cuts. Sometimes all it takes is running the thread again without adjusting. I get my threads tight and smooth right to the end of thread. It's not rocket science, but it does take patience and attention to detail.

If you have to remove metal from the muzzle threads to get a muzzle device to fit, using this rifle as a suppressor host is likely a bad idea.