Armalite AR10 muzzle threads

[Big_Country44]

I recently purchased an Armalite AR-10A with the 16" Government profile barrel. I ordered an AAC 51T muzzle brake for it and upon install discovered the threads on the barrel are too long and bottom out long before the brake reaches the shoulder of the threads. Is this an AAC problem or an Armalite problem? Would a different muzzle device work?

 

[GhostFace]

I’ve had at least 5 Armalite barrels and all were threaded properly but thats not to say your threads are correct. Take it to a gunsmith if you can’t measure your threads.

 

[Xcount]

Are you saying Armalite is supposed to coordinate with AAC when they build barrels? That's not how it works.

Shims are made for a reason. your AAC should have come with some to time it to any barrel.

 

[Im2bent]

How much gap are you seeing?

 

[Big_Country44]

Are you saying Armalite is supposed to coordinate with AAC when they build barrels? That's not how it works.

Shims are made for a reason. your AAC should have come with some to time it to any barrel.

Even after adding all the shims included with the brake, there's about 1/32 worth of visible threads. Mainly wondering if Armalite was known to have longer threads than usual or AAC muzzle devices were threaded shorter. Don't want to go spend another $100 plus on a different brake that still doesn't work

 

[redneckbmxer24]

Are you saying Armalite is supposed to coordinate with AAC when they build barrels? That's not how it works.

Shims are made for a reason. your AAC should have come with some to time it to any barrel.

There’s pretty standard specs for how long the muzzle threads should be for any given diameter and pitch, so you don’t know how it works either

 

[msgriff]

Machinist's general rule of thumb is the minimum thread length is equal to the major diameter. For 5/8x24, Thunder Beast specs a minimum length of 0.600" from the shoulder, AAC is 0.620". Neither manufacturer spec a maximum, but those numbers might help. There are also specs for relief cuts and maximum radius where the threads end at the shoulder, but since you're using shims, that might not be your issue. Some shim kits include 1) thick spacer shim, maybe 0.025", in addition to the normal shims.

 

[Xcount]

There’s pretty standard specs for how long the muzzle threads should be for any given diameter and pitch, so you don’t know how it works either

Shims. That’s how it works.

 

[Big_Country44]

Machinist's general rule of thumb is the minimum thread length is equal to the major diameter. For 5/8x24, Thunder Beast specs a minimum length of 0.600" from the shoulder, AAC is 0.620". Neither manufacturer spec a maximum, but those numbers might help. There are also specs for relief cuts and maximum radius where the threads end at the shoulder, but since you're using shims, that might not be your issue. Some shim kits include 1) thick spacer shim, maybe 0.025", in addition to the normal shims.

So I should be good if I order a shim kit with a spacer shim? Its not going to misalign the brake? A suppressor will be used occasionally

 

[msgriff]

So I should be good if I order a shim kit with a spacer shim? Its not going to misalign the brake? A suppressor will be used occasionally

As long as your spacers and/or shim stack still allows for the minimum muzzle thread length, then you're good to go. For most muzzle devices, you can usually go up to 1 rotation less than minimum muzzle thread length to allow for timing shims. 1 rotation at 24 TPI is 0.0417". There are a few installation and alignment procedures that I do, but everyone has their own way of doing things.

 

[Im2bent]

So I should be good if I order a shim kit with a spacer shim? Its not going to misalign the brake? A suppressor will be used occasionally

As long as you use shims and not crush washers everything should stay straight
https://www.midwayusa.com/product/1025478816?pid=752345 this one is 5/8