Need some advice here.  I just got in a Rainier Arms match barrel today and a brand new Surefire muzzle brake yesterday.  After installing the barrel I began the process of getting the brake timed properly.  It was a tight fit so I confirmed that both the brake and barrel were 1/2 x 28, which they were.  I put some oil on the threads and slowly worked the brake on, stopping when things got tight and backing off a turn then tightening further.  It was tight but nothing I wouldn't attribute to tolerances.  I removed the brake which came off easier than it went on and looked for burrs or anything on the threads, all looked clear.  I then went to reinstall the brake to determine which shims I would need to add to time it properly and it seized up on me 1/8" shy of full seated.  I've added penetrating oil and at this point I know the threads are wet but it won't move more than about a half turn in either direction.

I've got it in the freezer now.  The only thing I know to try is to get it good and cold then hit the brake with a MAP torch to heat it up quickly to see if that will allow it to come off.  Any other suggestions?

Carnage

Almost looks like the brake was short threaded or the barrel shank was too long.

Took some measurements but I don't know if these are indicative of what they issue may have been.

Unaffected OD of the barrel threads


Unaffected ID of the brake

I agree (or the threads inside the Surefire were damaged...,but I've put on a bunch of those and never had a bad one )

How long is the threaded section of the barrel (including the now damaged area)?

From the crown to the shoulder measures .6650"

I bought a barrel from Rainer with the muzzle threads out of spec.  I sent it back and they took care of me.  Give them a call and see what they say.

I sent them an email through their site.  They've got a great rep for CS so I'm hopeful they'll replace this barrel.

Spec for 1/2 x 28 is .620. I have found that some devices are short threaded so when I thread a barrel I typically go to .600.
The brake is fine, the SureFire stainless is hard as hell and the only time I have seen one damaged is when the remnants of a hardened pin rolled the first 3 threads.
The barrel is saveable, a couple of different things can be done.
1- cut back, re crown and thread.
2- cut the barrel back removing only the damaged threads, re crown and turn the barrel back enough to get you to .600. Pick up the existing good threads and thread the remainder.
3- turn down the shank and fabricate an oversized bushing, silver solder it on and turn and thread as normal.

Spoke with Rainier today.  They had received the barrel and were ready to replace it or possibly upgrade (I had mentioned that as a possibility).  They upgraded for the price difference and now I've got an Ultramatch barrel on the way.  They handled it as well as could be expected and I have zero complaints, they'll see more business from me in the future.

When I cut threads (5x a week) I fit the muzzle devise to the threads. I make sure the customer knows that I need the brake/comp to fit the threads correctly. If they do not have the one they want. I fit them to the A2 flash hider.

Not necessarily. Depends on where you want to index from, shoulder or muzzle. That being said,

Unforgivable mistake....

Rainier needs to fire the company making barrels for them or hire someone who knows how to use a thread ring gauge and check those crapastic stainless barrels before they hit the street. If the manufacturer can't make 0.500-28-UNEF-2A threads on a modern turn center, what does your chamber look like? Just sayin'...