Hey there, I built myself a nice SPRish build last winter and had quite a hard time installing my AAC flash hider.  Turns out the guy who cerakoted my barrel and FH sprayed it ON THE THREADS.  What a champ.

I had to fiddle around screwing and unscrewing the FH a bit at a time to loosen the cerakote stuck on the threads...a painfull process.  In the end I just put some MS 33 grease on them threads to finish the job....*sigh*

So last weekend I received my Precision Armament SPR 11 muzzle brake so I go on about removing my AAC FH.  It was some kind of a pain, but less than when I put it on.  I then clean the threads with 99% isopropyl and a paper towel, as well as with a nylon brush to get any crud (cerakote shavings and old grease) out.

I then proceed to screw the brake on by hand, but immediately notice that it jams after about 2-3 turns...now I read that you should be able to spin a muzzle device freely until you hit the end of the threads...right?

I'd say the first third of the threads seem clean/bare metal now, and the other two thirds seem a bit dark, maybe because of the cerakote getting into the metal's "pores"...?  Maybe the threads are in fact out of spec?!?

I do have to say that I initially (with the AAC) had to put on an insane amount of torque to get this thing on...didn't use a torque wrench but I was almost putting my whole weight on the wrench, so-to-speak.  And now, guess what?  My new brake is effing stuck halfway on the threads.....it just won't budge...

I don't know if I should be pissed about the careless cerakote job, or at Rainier Arms for having a defective barrel/threads?  Now I fear that I might've applied too much torque on the whole thing, I'm using a upper vise, not a barrel vise...I don't wanna screw (pun intended) with the barrel indexing...

If you do not have a barrel clamp you can always clamp the barrel between 2 pieces of wood in your vice. It will kind of indent and mold to the barrel when you tighten the vise. Make sure to clamp as close to the muzzle as possible. Then you should be able to get enough torque on the muzzle device to break it free without messing up the upper/ barrel indexing pin.

You should be pissed about the careless Cerakote job.  
My guess is that there was still some Cerakote in the threads.  When you added the Aeroshell, you gave the FH juuuuust enough lubrication to allow it to cross-thread as you torqued it on.  
Yes, the muzzle device should be able to screw all the way on with little to no effort.  That was your first sign something wasn't right.  

So far, it's not the end of the world.  But if you keep torquing on your barrel without having a barrel vice, you're gonna end up either bending/shearing your index pin or you're gonna warp your upper receiver.  
Your best bet at this point is to stop and take your upper to a gunsmith.  They can clamp your barrel, remove the FH, and then chase and clean up your threads with a thread cutter to remove the paint and hopefully straighten out any damaged threads.  

You should have them chase the threads in the muzzle device, too.  There's a good possibility those threads are warped or damaged as well.  If you get lucky, they will be able to get both cleaned up.  
Worst case scenario, they can cut back your barrel and re-thread.  How long is your barrel?  Is there enough to do this and still stay legal?

I will definitely stop and take the rifle to the gunsmith...in fact the same one that did the cerakote job (he's really competent for everything else and besides, if it's his fault he's not gonna charge me).

I just talked to me on the phone and says he's gonna inspect the threads, and indeed most likely chase the threads (he has a fully equipped machine shop).  He told me that he had an experience with a few barrels where the threads were improperly cut and this sometimes happens when the manufacturer's cutting die becomes worn.  He took time with me on the phone and assured me he would take care of it.  He's gonna try my 2 muzzle devices on other barrels he has layin' around also, to see if their threads are still ok.

Being an SPR build, barrel is 18".  But then again I'm in Canada so we don't require tax stamps for SBRs.  But wa are restricted to shooting them only in approved ranges....I'd rather deal with paperwork lol.

I spray my cerakote on my muzzle threads.

If applied properly, cerakote should not hinder putting on a muzzle device.

Well I went to my gunsmith today and he had a helluva hard time removing the brake.  He heated it a bit, was almost putting his weight on the damn thing.  It finally came off after a while, and here's what we saw afterwards.



The threads were crushed...

In the end he guessed right; my Rainier Arms barrel's threads were out of spec.  He reworked them and told me that a good deal of metal shavings came off.  He told me that this sometimes happen when the die used in the CNC machine gets a bit dull towards the end of its life cycle, and so the threads are not cut as they should.  Anyhow, he fixed it and it wasn't even his fault!  The brake looks wonderful, BEHAVES wonderfully and all is good.

OP's barrel is fixed now, but for any other new shooters....never do what's in bold.

~8 ft/lbs of torque on the muzzle device is what's called for.  If your brake/flashhider requires more you need to clean the threads.

Excessive torque on the muzzle of a barrel will throw off groups or cause inconsistent shooting. I've seen it happen.