AR10 barrel nut problem

[Grizzman47]

I don't recall hearing about this issue before. I've assembled a couple large frame ARs, using Aero upper receivers and Aero handguards and barrel nuts without difficulty.

I replaced a standard Aero gas block with a Superlative Arms adjustable gas block on one of them when I installed a 6.5 CM barrel, so I don't think the gas block is positioning the gas tube at an incorrect height.

 

[rpol98]

As the gas tube does not contact the nut near either of the bends, and without the nut in place it aligns perfectly I'm seriously doubting that the gas tube is the problem. The barrel nut deflects the gas tube into the top "tang" of the clover-leaf hole. I should mention that this happens when a groove in the nut is aligned with the clover-leaf hole.

Perhaps the issue is the CMMG upper having a tighter than usual clover-leaf opening? Even if that is the situation, the fact that without the nut in place the gas tube slides thru the clover-leaf hole and into the BCG's gas key with no drag tells me that the hole in the upper is OK. I'm test fitting with the tube already pinned into the Superlative AGB.

If y'all need pics you're gonna make me clean the work bench. No way I'm showing a pic of it like it is now......

if, with the barrel nut installed, the gas tube is contacting the front edge of the barrel nut, in the groove, and then is aimed so that it contacts the top tang of the cloverleaf, then the Z-bend in the gas tube is not enough to get it up high enough so that the back-end of the gas tube enters the receiver parallel with the top of the barrel nut.

that tells me it's an AR-15 gas tube, Z-bend for the smaller AR-15-sized barrel nut, insufficient offset in the Z-bend to clear the larger diameter of the AR-10-sized barrel nut.

if you want to use that gas tube, you're going to have to tweak it a little so that the final angle at entry into the clover leaf is perfectly parallel to the top surface of the barrel nut. not tilted up, as in your case. It's an easy remedy.

if your handguard slips over your barrel nut, then the barrel nut OD is in-spec.

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ETA: I'm not even sure if anybody even sells AR-15-length gas tubes (carbine, mid, rifle) for use in large-frame DPMS LR-308 application, because everybody just bends it a little to make it fit when necessary. It would be such a small niche market, although probably a bigger market than the Armalite AR-10 gas tubes (about 3/8" longer), which is a really really small market segment, probably kept alive only by Faxon AR-10 barrel sales. and Wilson Combat AR-10 barrels.

 

[squirrelslayer]

Again, when building an AR10, not all parts are compatible, hence why you need to stick with one maker and use their parts. AR15's you can mix and match, but AR10's are a pain in the butt.

AMEN!

 

[Stonyman88]

Parts are: CMMG upper, Aero M5 hand guard, Superlative AGB, Somebody's nitrated gas tube, Lothar-Walther barrel.

Everything screws together like it should right up until I try to install the gas tube. Even when perfectly aligned the grooves in the barrel nut are not deep enough for the gas tube to fit thru the clover-leaf opening. With the barrel nut removed the gas tube inserts like it is supposed to and goes into the gas key on the BCG as well.

Just wondering if this is a known problem, or I've got a weird one.

Mark the correct hole , take it off and mill it deeper by .010 to start, or measure it then mill some of the holes out

 

[lyle2231]

Atlas S-One. Nut looks the same as yours. Gas tube installs, fits, and floats as it is supposed to w/o the barrel nut in place.

I'll see what Aero has to say, just submitted a request.

Keep us posted

 

[Splitt]

Let me preface with I've not personally built one. So I could be just talking out my ejection port.
Personally, would not be dremeling the barrel nut. It just seems like weakening the structure to me. Have you considered getting a new gas tube from Aero?
Can you tweak the bend with a pipe bender to fit?
These seem the cheaper way to fix the issue than taking a grinder to a $200+ barrel nut.

 

[Darryle]

Some gas tubes are not correct, do you have an alignment pin?

What length has system? Shorter gas lengths have had me tweaking the unbranded cheap gas tubes.

I will send you a alignment pin to check it out, you can do the same thing with drill bit, measure your gas tube where it is swaged and get a drill bit.

PM your address and I will be glad to loan you my alignment pin, will even ship it out priority mail so it's not holding you up long. I can send you some #15 drill bits you can keep

 

[BigNate]

If you start bending the Z bend to gain height be very gradual. Changing the Z bend changes length at the same time.

 

[ntsqd]

I am satisfied that the BCG's gas key is aligned with the clover-leaf hole.

Without the nut in place the gas tube slides into the correct position all of the way into the gas key with the AGB sliding on the barrel's GB journal. In doing this I am holding the assembly by the AGB only, The opposite end of the gas tube is at the correct elevation to go thru the clover-leaf hole without my needing to nudge it in any direction. Eyeballically it is also parallel to the barrel in this section.

With the barrel nut in place, and with the gas tube / AGB assembly rotated 180° so that the AGB isn't being influenced by the barrel the gas tube will not fit thru the clover-leaf hole.

The gas tube is not the problem!

The groove in the barrel nut is not deep enough. I knew this when I first posted. What I wondered was if this was a known problem or if I had a Monday morning / Friday afternoon part.

 

[Citified]

I have assembled several AR-10s, both Armalite and DPMS and have never run into this situation. Depending on the answer you get about the barrel nut, I agree the simple solution is to slightly dremel the notch and run it. Not really an operational risk. I am willing to bet this particular nut is just slightly made out of the correct depth on the notch. I would like to hear the final answer as to what you do. Sounds like everything else is lined up correctly on the gas tube. I assume you verified it is a -10 tube?

 

[Darryle]

I have a 1/2 dozen uppers wearing either a R-One or S-One handguard and I haven't had an issue with interference when using my standard CMC gas tubes.

If the handguard slides over the nut and it's a groove issue, a quick call to Aero will get you the necessary dimensions to verify that.

 

[lyle2231]

I am satisfied that the BCG's gas key is aligned with the clover-leaf hole.

Without the nut in place the gas tube slides into the correct position all of the way into the gas key with the AGB sliding on the barrel's GB journal. In doing this I am holding the assembly by the AGB only, The opposite end of the gas tube is at the correct elevation to go thru the clover-leaf hole without my needing to nudge it in any direction. Eyeballically it is also parallel to the barrel in this section.

With the barrel nut in place, and with the gas tube / AGB assembly rotated 180° so that the AGB isn't being influenced by the barrel the gas tube will not fit thru the clover-leaf hole.

The gas tube is not the problem!

The groove in the barrel nut is not deep enough. I knew this when I first posted. What I wondered was if this was a known problem or if I had a Monday morning / Friday afternoon part.

Take a jeweler's file ; to the depth that is needed
complete build, go shoot/have enjoyment!
Just my 2c

 

[Mike6158]

not a common issue, but does exist from time to time, nothing a dremel can't fix

Brownell's did a video about this problem and they said the same thing. Careful work with a Dremel will fix it.

 

[BigNate]

I've only built two large frame ARs so not a lot of knowledge, but I didn't have any issues either.
If ithe interference is minimal I'd clearance it being careful not to create to much heat, and March on.