Alexander Arms Barrel Extension unscrewed itself - easy to fix?

[lazyengineer]

After about 300 rounds, my Alexander Arms 20" HBAr stated shooting erratically . And when warm at all, the barrel would wiggle very noticeably. Wait a couple minutes and it cooled back down, and it would tighten up. Very odd.

So I pulled it off, and the barrel extension is loose, and unscrewed easily in my hands.

I contacted Alexande Arms, who offered to fix it, but since its 8 months old, they are refusing to pay shipping - which I think is kind of poor customer service personally - to me that's a factory defect.

So I'm wondering how easy is it to fix something like this yourself? I'm guessing my timing will be off if I screw and torque it back on myself? And also, my headspace would change too?

I'm not poor, I can pay the shipping. just a little irked that I have to do so with a factory defective item. Is this normal for Alexander Arms?

Thoughts on best route from here?

[LRRPF52]

I think that’s the 2nd one we’ve heard about.

The torque on a barrel nut should be so high, there is no way it would come undone like that under fire.

Did you use a reaction rod when installing it or apply torque to the barrel/barrel extension when un-installing a muzzle device?

There have been more cases of this happening on other AR15s once people started using reaction rods for muzzle device work.

[lazyengineer]

Thanks for the reply. No, I don't have nor use a reaction rod (which I had to look up just now even). Muzzle device is a just a basic flash-hider, and was installed with just a few foot-lbs; so that shouldn't mess anything up.

[Klem]

I'm guessing my timing will be off if I screw and torque it back on myself? And also, my headspace would change too?

Thoughts on best route from here?

Lazy,

AA would have headspaced the chamber with the extension torqued up tight.

I have always understood 150ft lbs is the MILSPEC torque for an extension. I read different torques from 100 - 150ft lbs on different forums, more towards 150 however.

I came across this on Homegunsmith forum which discusses how headspace varies between screwed on with no torque, and screwed up to 140.

[INDENT]It's 140 ft-lbs, and you have to kinda wing it - in general about 0.0035" (or two pieces of scotch tape on the back of your headspace gage) is good. If the 'go' guage fits with two pieces of tape on the back, it will likely fit (without the tape) after the extension is torqued into place... you should certainly verify that it's correct, but you can always go back and make small adjustments - like cutting the chamber a few thou deeper by hand if you underestimate, or taking a little off the shoulder if you over estimate.
[/INDENT]

To be clear, you mention "barrel extension", not barrel nut so you mean the extension with bolt lugs and indexing pin that screws onto the barrel and done at the factory, right? Not the barrel nut that screws the barrel and extension into the upper.

[lazyengineer]

Correct - not the nut, but the dadgum extension. where the lugs are. Never messed with that before, since those always come barrel pre-installed.

[lazyengineer]

Sent it back. Ate the $17 it cost me to do that. Not overly impressed with Alexander Arms customer service right now.

[Double Naught Spy]

I had one come apart on my 16" AA upper. I was trying to get the muzzle device off so that I could use it with my suppressor when it came loose. A buddy of mine took care of it.

[tdbru]

to keep the torque off of the extension / barrel junction when messing with muzzle devices, it's best to put the barrel in a barrel vise. if you have one. then no torque from messing with the muzzle devices is transferred to the extension / barrel junction

lacking that you might try and drill a hole through a block of wood that is the diameter of the barrel behind the muzzle device. cut it in half through the hole, and then use a bench vise to clamp the barrel into the two halves of the block of wood securing the barrel so it won't rotate while you swap muzzle devices. easier of course if you take the upper off and the bcg/handle out before you start.

be wary of reaction rods for swapping out muzzle devices as your counting on the barrel extension torque into the barrel to be greater than the torque it takes to remove / install a muzzle device. that is if the pin isn't drilled into the barrel, but only into the barrel extension. i know a lot of folks have successfully used them, but the only way i am aware of to absolutely keep all torque off of the barrel/extension/pin/upper junction is to put the front of the barrel in a barrel vise. then the barrel vise / barrel junction takes all the torque from changing out muzzle devices. there will be 0 torque on the barrel/extension/pin/upper junction with the barrel vise.

some rosin helps with the barrel vise inserts or wood blocks to keep the barrel from spinning in the barrel vise.

-tdbru

[A5BLASTER]

And this is why I use the accuwhaser system and time my muzzle devices to be set by hand with no tools needed other then my BEV block to hold the upper in the vice.

[Mad Charlie]

And this is why I use the accuwhaser system and time my muzzle devices to be set by hand with no tools needed other then my BEV block to hold the upper in the vice.

Same here, and I also got an improvement in accuracy in one of my rifles.
A little more money, but worth it in my opinion.

[montana]

Same here, and I also got an improvement in accuracy in one of my rifles.
A little more money, but worth it in my opinion.

Here is another solution. https://www.wingtactical.com/firearm-par...-lock-nut/

[lazyengineer]

to keep the torque off of the extension / barrel junction when messing with muzzle devices, it's best to put the barrel in a barrel vise. if you have one. then no torque from messing with the muzzle devices is transferred to the extension / barrel junction

lacking that you might try and drill a hole through a block of wood that is the diameter of the barrel behind the muzzle device. cut it in half through the hole, and then use a bench vise to clamp the barrel into the two halves of the block of wood securing the barrel so it won't rotate while you swap muzzle devices. easier of course if you take the upper off and the bcg/handle out before you start.

be wary of reaction rods for swapping out muzzle devices as your counting on the barrel extension torque into the barrel to be greater than the torque it takes to remove / install a muzzle device. that is if the pin isn't drilled into the barrel, but only into the barrel extension. i know a lot of folks have successfully used them, but the only way i am aware of to absolutely keep all torque off of the barrel/extension/pin/upper junction is to put the front of the barrel in a barrel vise. then the barrel vise / barrel junction takes all the torque from changing out muzzle devices. there will be 0 torque on the barrel/extension/pin/upper junction with the barrel vise.

some rosin helps with the barrel vise inserts or wood blocks to keep the barrel from spinning in the barrel vise.

-tdbru

A viceblock was used for the ~5 ft-lb of muzzle device torque. I don't have a reaction-rod.