Problem with barrel nut

[flenna]

While installing the barrel nut I cannot get a slot to line up with the gas tube hole. At 30 ft.lbs. it just barely covers the hole enough where the tube will not go in straight. But I cannot tighten the nut enough for it to open up- I can muscle it to 80 ft.lbs but it will not open it all the way up. Any suggestions?

[556Cliff]

Standard GI barrel nut or something else? In either case it's best to try a different nut or a different receiver. However, I've had the same experience of being just past alignment with GI barrel nuts and I still always manage to get there at the high end of the torque spec with tightening and loosening (not all that excessively either).

Key things that might help: Lube, don't be shy with it. Liberally apply it to the threads of the upper and the forward facing side of the barrel extension flange. Also, inside on the threads of the barrel nut is fine too, but it should be nowhere else.

I personally use a high moly content paste and not the the AeroShell stuff. This might make a difference in things always working out for me. I'm not saying you should use it, but it's what I use (TS-70 moly paste).

Also, a good barrel nut wrench can make a hell of a difference in reaching alignment at or near the max torque value. As far as I'm concerned, the barrel wrenches from 2UniqueLLC are the only ones I care to use on standard barrel nuts. And you need to secure the receiver in a solid vise setup. I use a Wilton Bullet machinist's vise, mounted to a very solid bench bolted to the concreate floor. I also (usually) clamp the upper receiver in clamshells with a fin topped reaction rod (in my case I prefer the one from 2UniqueLLC) used inside the receiver as support, but this also locks the barrel extension solid with the receiver so that the barrel extension cannot twist in the receiver while the barrel nut is being tightened and loosened and tightened again. I do shim the fin on the 2UniqueLLC reaction rod with those clear plastic snare drum strainer strips so that there is no play inside the receiver so that the FSB stays in perfect alignment. That is if the FSB was in perfect alignment to begin with before tightening anything down.

See the below video for some idea as to the method.

[HKGuns]

While installing the barrel nut I cannot get a slot to line up with the gas tube hole. At 30 ft.lbs. it just barely covers the hole enough where the tube will not go in straight. But I cannot tighten the nut enough for it to open up- I can muscle it to 80 ft.lbs but it will not open it all the way up. Any suggestions?

Shims.

Read this and see if it helps you out

Sometimes a different barrel nut will work, but shims will allow you to work with what you have.

[Waylander]

^^ Get shims in your life and don’t look back.

[flenna]

So it looks like shims may be the way to go. However, I am assuming the barrel nut will need to be removed to add the shims? The barrel has a FSB installed so it would end up being a bigger job than I hoped for. Note- this is my first AR built from stripped receivers so I am new to this.

ETA: just read I can snip the shim to install without removing the FSB.

[HKGuns]

ETA: just read I can snip the shim to install without removing the FSB.

Yep, you got it.....

If you have further issues, ask away. Chances are I've probably screwed it up before and learned a hard lesson that may save you some trouble.

[bobcatdriver]

So it looks like shims may be the way to go. However, I am assuming the barrel nut will need to be removed to add the shims? The barrel has a FSB installed so it would end up being a bigger job than I hoped for. Note- this is my first AR built from stripped receivers so I am new to this.

ETA: just read I can snip the shim to install without removing the FSB.

Go to Bison Armory. Nice video on installing the shims.

[flenna]

Go to Bison Armory. Nice video on installing the shims.

I ordered the shims from them and watch the video. Although what they show seems counterintuitive to maintaining headspace- they show installing the shims between the barrel extension and receiver as opposed to the barrel nut and extension.

[Waylander]

I ordered the shims from them and watch the video. Although what they show seems counterintuitive to maintaining headspace- they show installing the shims between the barrel extension and receiver as opposed to the barrel nut and extension.

The receiver shims won’t affect headspace. I just like the idea of the barrel nut shims better so I went with those.

[556Cliff]

I ordered the shims from them and watch the video. Although what they show seems counterintuitive to maintaining headspace- they show installing the shims between the barrel extension and receiver as opposed to the barrel nut and extension.

That won't effect headspace. But, it's how you have to use them if you cut the shims (which you have to to get around the indexing pin). They cannot be placed between the barrel nut and the barrel extension flange if they are cut, as the shim will bunch up on itself and become damaged. You can only stick them between the barrel nut and barrel extension flange if they are solid as they come.

Now something that can happen when using a cut shim between the receiver face and the barrel extension flange is the bolt carrier will seat ever so slightly forward. Usually it's not enough to make any difference, but you could run into the issue of the buffer impacting the buffer retainer pin if things were already a bit too close to begin with.