AR Rebuild - Problem Question

[1075tech]

I've put together more than a few without any issues that weren't my fault but I try to use parts of known quality. My first AR was pit together during one of the first "panics". I bought a complete upper off Gunbroker. 16", carbine length gas unknown barrel maker. It is only marked "L 556Nato 1:7".

From the beginning, I had some issues. First, I had to move the rear sight all the way left to get it zeroed. Second, I was blowing primers and getting heavy ejector swipes. Not every time, but maybe 20%. Different brands.

The first issue I'm assuming is that the upper face is not square. I use a Wheeler tool to square the receiver face. I also bed my barrels with loctite.

The second issue, I'm thinking maybe over gassed or chamber issue. It's either over pressured or unlocking too early from what I can figure.

It sat in the safe for quite a while. Yesterday, I started tearing it down. It has the regular front sight. I didn't want to remove that so I only remove the gas tube. When I went to loosen the barrel nut, the whole barrel turned. I was able to unscrew the barrel from the extension by hand. Welp, that's not good!

I'll square up the face of the receiver next.

My question is, what is the minimum torque required for the extension? And wouldn't putting the extension back on require it to be head spaced again? I've never taken one down that far before. Might be easier to just replace the barrel.

 

[kev74]

Min barrel torque is 35 ft/lbs. Then tighten till the next a lot for the gas tube is squared up. If your barrel nut wrench extends the length of your torque wrench, take that into consideration.

The barrel / bolt headspace shouldn't be effected since the bolt seats and locks in the barrel its self.

 

[1075tech]

Min barrel torque is 35 ft/lbs. Then tighten till the next a lot for the gas tube is squared up. If your barrel nut wrench extends the length of your torque wrench, take that into consideration.

The barrel / bolt headspace shouldn't be effected since the bolt seats and locks in the barrel its self.

Are you talking about the barrel nut or the barrel extension? I'm familiar with the torque for the barrel nut. But I shouldn't be able to unscrew the barrel from the barrel extension by hand! I had to use my torque wrench to get the barrel nut loose, AFTER the barrel was already removed. I'm pretty sure the barrel isn't supposed to come out in two pieces.

 

[kev74]

Hmmmm.... I've never seen a barrel extension come loose. Any I've done were as assemblies. I'm stumped.

At least you found your sight alignment issues.

 

[1075tech]

I got my google-fu on and did some reading. 150 ft lbs for the barrel extension. BUT have to make sure it is in the exact position for the indexing pin and the gas port to be in alignment. Probably just strip off the A2 and the FSB and pick up a barrel of known quality. Even if I mess with the extension, I still don't know about the possible chamber issue.

 

[Exonautic]

Damn, that's new. I've never had or even heard of an extension coming lose. Better off just getting a new barrel.

 

[Eddie Gunks]

If the barrel extension is loose it WILL need to be head spaced.

Get a new barrel

 

[1075tech]

Yep. New barrel is what I was thinking. Bury this one to throw off the metal detectors.

 

[fnfalguy]

@1075tech drop me a line. I should have a spare BA barrel and I think it has a nekkid muzzle.

 

[Exonautic]

I also got a spare threaded I'm looking to sell so if that's your preference let me know

 

[dsdmmat]

I got my google-fu on and did some reading. 150 ft lbs for the barrel extension. BUT have to make sure it is in the exact position for the indexing pin and the gas port to be in alignment. Probably just strip off the A2 and the FSB and pick up a barrel of known quality. Even if I mess with the extension, I still don't know about the possible chamber issue.

yeah bad juju for a barrel extension to be loose. I have made an AR barrel from a bolt gun barrel before and the extension has to be torqued on to properly chamber and headspace it to the bolt.

 

[Mosinitis]

Don't waste your time squaring up receiver face. It doesn't do anything good to speak of. The reason your alignment between front and rear sights was off is not the face of the receiver. What you had is a known problem, that happens when wrong tools are use to torque on the barrel nut. This was so common that I think Bushmaster had a video on it, but I am not sure. The proper way to install a barrel is to use a clam type block to hold the receiver in a vise. When installation is done by clamping the barrel in a vise or using Guisselle reaction rod, it can bend the indexing pin on the barrel extension and lead to misalignment between the sites you described.

The fix for this problem was somewhat gruesome. Clamping the upper receiver in a vise and hitting front sight with a mullet.

 

[1075tech]

Don't waste your time squaring up receiver face. It doesn't do anything good to speak of.

Whether it does any good or not is open for debate. It doesn't hurt anything and only takes a few minutes. Upper receivers can, and do, have issues with the face not being square to the extension. This will cause a left/right misalignment between the sights. I know I've done it on the builds that I have done, and they are all sub-MOA rifles with factory ammo. I'm not saying it is because of this though. Just that it can't hurt.

When installation is done by clamping the barrel in a vise or using Guisselle reaction rod, it can bend the indexing pin on the barrel extension

I would think that the aluminum upper would give before bending a steel pin. The use of the reaction rod is designed to NOT let the barrel/extension move. Unless you are talking about installing a barrel extension, then I don't know. I've never installed one. Or are you referring to installing the barrel nut? That I could possibly see as the nut will apply some torque to the upper receiver. In that case, see the first sentence.

 

[ProgSpear]

Don't waste your time squaring up receiver face. It doesn't do anything good to speak of. The reason your alignment between front and rear sights was off is not the face of the receiver. What you had is a known problem, that happens when wrong tools are use to torque on the barrel nut. This was so common that I think Bushmaster had a video on it, but I am not sure. The proper way to install a barrel is to use a clam type block to hold the receiver in a vise. When installation is done by clamping the barrel in a vise or using Guisselle reaction rod, it can bend the indexing pin on the barrel extension and lead to misalignment between the sites you described.

The fix for this problem was somewhat gruesome. Clamping the upper receiver in a vise and hitting front sight with a mullet.

LOL! Which style mullet should be used?



or




Sorry, didn't mean to prang the thread, but the imagery just struck me.

 

[Mosinitis]

I would think that the aluminum upper would give before bending a steel pin. The use of the reaction rod is designed to NOT let the barrel/extension move. Unless you are talking about installing a barrel extension, then I don't know. I've never installed one. Or are you referring to installing the barrel nut? That I could possibly see as the nut will apply some torque to the upper receiver. In that case, see the first sentence.

I am refering to installing or removing the barrel nut. Reaction rod should not be used. It's the opposite of what Guissele claims. If you think it through you will understand why. Receiver should be held by a clamshell block secured in a vise when the barrel and barrel nut is installed.

 

[Mosinitis]

I heard about barrel extension coming loose when reaction rod is used to hold the upper.

 

[Exonautic]

I heard about barrel extension coming loose when reaction rod is used to hold the upper.

When doing what? Torquing a muzzle device?
In theory I'd think it would be best to use a reaction rod when doing muzzle devices and a clamshell when doing handguards. In both cases you get the most contact surface for what you're doing. If a barrel extension is busting off there's a problem either with the barrel extension, or someone welded your muzzle device on with a mig welder because there shouldn't be that much torque on an MD.

 

[Mosinitis]

When doing what? Torquing a muzzle device?
In theory I'd think it would be best to use a reaction rod when doing muzzle devices and a clamshell when doing handguards. In both cases you get the most contact surface for what you're doing. If a barrel extension is busting off there's a problem either with the barrel extension, or someone welded your muzzle device on with a mig welder because there shouldn't be that much torque on an MD.

Barrel installation or removal. Muzzle device doesn't require a lot of torque, anything can be used.

 

[1075tech]

Clam shell for the barrel nut makes sense. That I can understand. The extension is supposed to be torqued to around 150. Maybe 20-30 for muzzle device. I was able to unscrew the barrel by hand. The flash hider was only slightly tighter. The barrel nut I'm going to guess at maybe 20-30, tops. It's a tomato stake now. New barrel on its way soon

 

[Mosinitis]

Clam shell for the barrel nut makes sense. That I can understand. The extension is supposed to be torqued to around 150. Maybe 20-30 for muzzle device. I was able to unscrew the barrel by hand. The flash hider was only slightly tighter. The barrel nut I'm going to guess at maybe 20-30, tops. It's a tomato stake now. New barrel on its way soon

Never had to assemble extension on to a barrel, so I don't have a clue. I would use clamshell for muzzle device as well, after the barrel nut is torqued on it's a strong assembly. Muzzle device doesn't require nearly as much torque as the barrel nut. In fact I hand tighten them with blue loctite, never had one come lose. The reason I do that, it doesn't put stress on the barrel end and improves accuracy. That is a standard practice for building a competition service rifle.

 

[Mosinitis]

You should go with higher torque on the barrel nut 35-70. It will not be a problem with clamshell block. You whole problem was using reaction rod.

 

[1075tech]

You should go with higher torque on the barrel nut 35-70. It will not be a problem with clamshell block. You whole problem was using reaction rod.

It wasn't me. It was a no name upper I bought off gunbroker several years ago.

 

[Mosinitis]

It wasn't me. It was a no name upper I bought off gunbroker several years ago.

Weren't you using reaction rod to disassemble?

 

[1075tech]

After removing the gas tube, I set it up on the reaction rod to loosen the barrel nut. I was getting the AR wrench in place on the nut when I wasable to turn the barrel out of the extension. It was only hand tight.