So I was helping a buddy build his first AR.  I have built about a dozen myself, but we ran into an issue that I have never seen before.

He bought high quality parts.

Aero small parts, receivers, etc.

Epsilon muzzle brake with a crush washer.

He threaded on the muzzle brake by hand.  He did not cross thread it.  It went on smoothly.  No thread locker.  He hand threaded it down to the crush washer and only had to turn it 180 degrees beyond hand tight to index the muzzle brake.

He has fired it, maybe 50 times.  He decided to swap out his had block for a JP adjustable.  So today we went to remove his brake so that we could remove his gas block.  It initially moved like you would expect.  A bit of tension to release the flex from the crush washer.  Then it started to get progressively harder and harder to unscrew.  He did not torque it the wrong way.  He did not over torque it when he first installed it.

The amount of tension became so great that we stopped because we didn't want to damage something.

So what happened?  Broken threads?

I'm not sure why it became hard to remove? I would suggest tightening and loosening it a half turn or so back and forth over and over again, gradually remove it a little bit more each turn. See how that goes.

Possibly a burr in the threads causing galling.

worse case - cut it off carefully with a Dremel and then chase the threads with an adjustable 1/2x28 die. Run loose and progressively tighten the die until you are certain you fixed it.

I am afraid the threads are going to be fucked.

https://www.vg6precision.com/vg6-gamma-556-bbss

Instructions on the vendor page for that brake suggests using anti-seize.  I didn't do the shopping so it didn't occur to me.  I am familiar with the concept of galling but honestly didn't even give it a consideration in this case.  All of my stainless barrels have had a finish of some kind, ion bond, etc.  And I haven't ever used a stainless muzzle device on a naked stainless barrel.

Looks like his options are going to be sending it to ADCO for shortening, threading, and then pin and weld a new muzzle device.

I'm afraid the threads are already too damaged to salvage.

Tried that with some penetrating oil as well.

If I had expected any kind of an issue, a soak with some penetrating oil for an hour or two before removal probably would have prevented this.  

I believe this is correct.

Yeah....I use oil or grease for all MDs.

SS to SS.......regardless of application, this always finds it's way into the process:

Attached File

I'm gunna say it could be cheap stainless.  Ran into this numerous times on transformer spade bolts.  The manufacturer eventually got it figured out but not before a bunch of fuct up transformers.... Anti seize may help but it's not a for sure.  It's the galling when it gets hot and is torqued tight.  It almost turns into a weld.

Sounds like it was galling.  If he kept turning it when it was getting harder and harder to rotate, he probably screwed himself.

Try lube first, let it soak a long time before attempting again.  If that doesn't work, I'd cut it off or try heat.

It most likely was just a burr to start with.  Clean your threads first next time.

No, anti seize is definitely not a for sure. Definitely a prevention worth practicing.

As always with SS to SS....any tension/resistance is likely going to be an issue. Inspection prior to mating is key.

This is correct.  SS to SS loves to gall so proper fitment and lube is critical.  Grade of SS seems to matter little.  The application of heat actually will make galling worse.

If the barrel and MD were SS then the only fix is to cut it off, rethread, and recrown.  Anything less will end in more frustration.

Too late for the penetrating oil, the damage would have happened when tightening.

The lubrication I use when assembling stainless to stainless is TefGel and Vaseline 50%/50%.

TefGel is made for stainless on aluminum but works well for stainless on stainless in my experience.