AR10 barrel nut problem

[ntsqd]

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 M.]

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

 

[rpol98]

I don't recollect having that problem when I did my Aero M5 build, last year. sorry, don't have a pic of front view, gun is assembled now. When i lock the bolt back, i can jiggle the gas tube with a screw driver through the top slot, which indicates there's some wiggle clearance in the "cloverleaf", i.e. gas tube is not binding against the barrel nut.

 

[Darryle]

There are various heights of DPMS style uppers, Aero M5s are high profile

DPMS 308 Upper heights

 

[Darryle]

Found this on CMMG's resource page, do you know if you have a Gen 1 or Gen 2 CMMG upper?

CMMG Resource Page

Gen1 is the more prevalent of the two sets of specifications, despite it being longer and therefore heavier than Gen2. Gen1 and Gen2 are not compatible with each other, either. Gen1 also has a set of sub-specs for its upper groups. They are commonly referred to as High Profile and Low Profile, referring to the height of the tang on the Picatinny rail, where the charging handle is installed. High Profile and Low Profile handguards and upper receivers are not cross compatible with each other, either. For the record, CMMG's Mk3™ is a Gen1 DPMS High Profile platform, and it is available in .308 WIN (this can also utilize the 7.62x51 NATO cartridge) and 6.5 Creedmoor.

 

[waveslayer]

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.

 

[ntsqd]

The thing that seems to being missed here is that the clover-leaf hole has to be in the same location regardless of High or Low upper receiver because there is really only one DPMS pattern BCG (no idea how the Armalite pattern BCG compares but I don't have one of those). Which means that the gas tube has to be in the same place regardless, which in turn implies that the barrel nut is wrong. Not something that I expected from Aero. FWIW the rail on the upper and the rail section on the hand-guard align perfectly.

I am just curious if this is a known problem or not. I had not seen anything about it in my admittedly limited searching. I could correct it with a ball-nose endmill, but I think that I'll see what Aero has to say first.

 

[rpol98]

The thing that seems to being missed here is that the clover-leaf hole has to be in the same location regardless of High or Low upper receiver because there is really only one DPMS pattern BCG (no idea how the Armalite pattern BCG compares but I don't have one of those). Which means that the gas tube has to be in the same place regardless, which in turn implies that the barrel nut is wrong. Not something that I expected from Aero. FWIW the rail on the upper and the rail section on the hand-guard align perfectly.

I am just curious if this is a known problem or not. I had not seen anything about it in my admittedly limited searching. I could correct it with a ball-nose endmill, but I think that I'll see what Aero has to say first.

agreed on the bolded part, above.

so does your barrel nut look the same as mine? or are you not running the Atlas series of rails? pics?

 

[ntsqd]

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.

 

[rpol98]

my barrel requires the use of an Armalite AR-10 gas tube. If you're using an AR-15 gas tube, maybe the bends don't allow for the extra length of the AR-10 barrel nut? So maybe your gas tube is making contact with the front edge of the barrel nut?

hard to imagine, if your barrel nut looks the same as mine, and yes, the clover leaf has to be in the same position, LR-308 DPMS standard, somehow, your Aero Atlas barrel nut has a larger diameter so it obstructs a straight shot to the clover leaf?

yeah, something doesn't add up.

 

[Darryle]

Without the nut in place, barrel installed, does it align properly?

I realize about the height, but having used several of the R-One and S-One M5 handguards with Aero M5 uppers and having no issues.

DPMS and PSA have given me enough issues, I never even consider them anymore.

I have a Wilson Combat receiver set, but they are based on the Armalite pattern.

 

[waveslayer]

I would bet it's the wrong gas tube

 

[ntsqd]

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......

 

[rpol98]

Pro Tip for the day: crop your pics to only show the area necessary.