Gas Tube / Barrel Nut Interference

[WestDesertPRS]

I'm building a new upper and am having an issue with my Gas Tube contacting the barrel nut. Not sure of this is a problem or not. I've built many rifles (15-20) over the years and never noticed this before.

Barrel is a Ballistic Advantage 20" Premium Series DMR profile. Gas block is from BA and is drilled for a roll pin to secure it to the barrel.

Handguard and barrel nut are Geissele Mk16 and Gas tube is Aero Precision rifle length.

Upper receiver is unknown...something I had in my parts bin.

Should I be concerned or just quit worrying and get it together?

 

[StaveyIL]

You could remove the gas block and gas tube . Then while still assembled carefully file the top of the barrel nut down a little bit down the centre to give a little more clearance .

 

[Molon]

You could remove the gas block and gas tube . Then while still assembled carefully file the top of the barrel nut down a little bit down the centre to give a little more clearance .

...

 

[Molon]

Should I be concerned or just quit worrying and get it together?

That depends. Do you want a shitty build, or do you want to do it right? Do you want to just put a band-aid on the problem, or do you want to correct the problem?

If you want to do things right, the first thing to do is verify that the gas tube channel in the mystery receiver is correctly located in the receiver.



....

 

[msgriff]

If you have clearance at the receiver end, but not at the muzzle end of the barrel nut, adjust the offset.

 

[StaveyIL]

...

Clearly I’m not there looking at it. However if the barrel nut is oversize , taking 1/16 off the top centre would make zero difference . I would want my gas key to line up perfectly with the gas tube . If that meant a tiny bit of filing. So be it.
Gas tube could be bent , lots of variables at play.

 

[msgriff]

Clearly I’m not there looking at it. However if the barrel nut is oversize , taking 1/16 off the top centre would make zero difference . I would want my gas key to line up perfectly with the gas tube . If that meant a tiny bit of filing. So be it.
Gas tube could be bent , lots of variables at play.

WECSOG

 

[StaveyIL]

LOL, If you build enough rifles you will realize that occasionally have to think outside the box . Sending things back isn’t always an option. I could have said send it back and buy quality parts. Either way I don’t care.
Happy Shooting.

 

[StaveyIL]

If you have clearance at the receiver end, but not at the muzzle end of the barrel nut, adjust the offset.

Irregardless of gas tube , gas key alignment ?
Please elaborate on how he should do this.

 

[msgriff]

Irregardless of gas tube , gas key alignment ?
Please elaborate on how he should do this.

There is no guarantee that a particular gas tube is bent correctly. It's up to the builder to verify the offset and whether the legs are parallel. As pointed out above, verifying that gas tube channel through the upper is also up to the builder (AR-15: 0.783" centerline of bore to center of gas tube channel). Then they would also check the carrier key to gas tube alignment.

 

[bigjake83]

I'm building a new upper and am having an issue with my Gas Tube contacting the barrel nut. Not sure of this is a problem or not. I've built many rifles (15-20) over the years and never noticed this before.

Barrel is a Ballistic Advantage 20" Premium Series DMR profile. Gas block is from BA and is drilled for a roll pin to secure it to the barrel.

Handguard and barrel nut are Geissele Mk16 and Gas tube is Aero Precision rifle length.

Upper receiver is unknown...something I had in my parts bin.

Should I be concerned or just quit worrying and get it together?

I've seen this a few times, and could be a few different issues.

What size diameter is your gas block?

Remove your gas block and tube and take the same picture you have above without the gas tube in the way With a clear view of where your gas tube enters your upper, and try to make the photo perfectly parallel in the center of the photo.

Basically it's going to be (3) things?

Out of spec Gas Tube?
Out of spec Upper?
Gas Block is too low?

I'm assuming you're running a .750 Gas Block?? And not a .625?? So I'll go out on a limb and say it's not the GB. So I'd buy a gas tube from a reputable vendor and if that doesn't fix the issue shit can the upper.

Do you have another upper you could disassemble to see if you still have the same issues on a separate upper??

 

[WestDesertPRS]

There is no guarantee that a particular gas tube is bent correctly. It's up to the builder to verify the offset and whether the legs are parallel. As pointed out above, verifying that gas tube channel through the upper is also up to the builder (AR-15: 0.783" centerline of bore to center of gas tube channel). Then they would also check the carrier key to gas tube alignment.

Thanks for the spec on gas tube channel measurement....something I didn't have.

Interesting thing is that the gas tube lines up perfectly fine with the channel. It doesn't have to be "forced" or tweaked to fit in place. It is just closer to the barrel nut than I'm used to seeing. It's barely resting on the nut, not putting a lot of pressure on it, but I'm used to a small gap.

I've installed rails from DD, BCM, MI, as well as some cheapos, but this is the first Geissele so I wasn't sure of this was normal or not.

 

[msgriff]

Thanks for the spec on gas tube channel measurement....something I didn't have.

Interesting thing is that the gas tube lines up perfectly fine with the channel. It doesn't have to be "forced" or tweaked to fit in place. It is just closer to the barrel nut than I'm used to seeing. It's barely resting on the nut, not putting a lot of pressure on it, but I'm used to a small gap.

I've installed rails from DD, BCM, MI, as well as some cheapos, but this is the first Geissele so I wasn't sure of this was normal or not.

I've also seen 0.781" being quoted as the spec, but I don't know what the tolerance is.

 

[WestDesertPRS]

I've seen this a few times, and could be a few different issues.

What size diameter is your gas block?

Remove your gas block and tube and take the same picture you have above without the gas tube in the way With a clear view of where your gas tube enters your upper, and try to make the photo perfectly parallel in the center of the photo.

Basically it's going to be (3) things?

Out of spec Gas Tube?
Out of spec Upper?
Gas Block is too low?

I'm assuming you're running a .750 Gas Block?? And not a .625?? So I'll go out on a limb and say it's not the GB. So I'd buy a gas tube from a reputable vendor and if that doesn't fix the issue shit can the upper.

Do you have another upper you could disassemble to see if you still have the same issues on a separate upper??

It is a .750 gas block. The gas tube is Aero Precision...I've used a lot of their small parts and had no issues in the past. You mentioned buying a gas tube from a reputable dealer...should I not be using AP?

As far as tearing down another upper...that's a possibility if it really becomes necessary.

 

[bigjake83]

it is a .750 gas block. The gas tube is Aero Precision...I've used a lot of their small parts and had no issues in the past. You mentioned buying a gas tune from a reputable dealer...should I not be using AP?

As far as tearing down another upper...that's a possibility if it really becomes necessary.

I'm not a fan of Aero, most the time their stuff "works" but it's not going to be winning any awards anytime soon for Best in Quality. The gas tube is the cheapest part to purchase again to try and eliminate what's causing this alignment issue, it's very easy for Gas Tubes to get bent in the shipping and distribution process..

Uppers and gas blocks are relatively inexpensive and roughly the same price so you're just going to have to choose which one to replace if you want to make your current setup work..

You can try another upper that is quality but won't break the bank?? BCM comes to mind.

Or get a taller gas block like the Wilson Combat pictured here..

Either way I'd still go through the hassle of disassembling another upper to compare notes here so you can find out what the culprit is in this situation.

 

[bfoosh006]

FWIW... most Adj. GB's will "present" the gas tube at a slightly higher position.

 

[WestDesertPRS]

I'm not a fan of Aero, most the time their stuff "works" but it's not going to be winning any awards anytime soon for Best in Quality. The gas tube is the cheapest part to purchase again to try and eliminate what's causing this alignment issue, it's very easy for Gas Tubes to get bent in the shipping and distribution process..

Uppers and gas blocks are relatively inexpensive and roughly the same price so you're just going to have to choose which one to replace if you want to make your current setup work..

You can try another upper that is quality but won't break the bank?? BCM comes to mind.

Or get a taller gas block like the Wilson Combat pictured here..

View attachment 8095229
Either way I'd still go through the hassle of disassembling another upper to compare notes here so you can find out what the culprit is in this situation.

What's your recommendation for a gas tube? BCM?

As far as the gas block, I won't be changing it since the barrel / block are already cross-drilled for a roll pin.

 

[bigjake83]

What's your recommendation for a gas tube? BCM?

As far as the gas block, I won't be changing it since the barrel / block are already cross-drilled for a roll pin.

For all my common gas tubes I order Spikes Tactical, Rainer Arms and Lantac gas tubes all of which are Nitride. Also when ordering from Rainer Arms they ship thier tubes in a heavy duty cardboard tubes to prevent any damage in shipping.

https://www.rainierarms.com/gas-tube-black-nitride/

If you're set on your gas block option I'd go ahead and pick up a BCM upper.

 

[WestDesertPRS]

Interesting reply from Geissele tech support about this issue. Apparently normal for their barrel nut...surprises me a little...

If I'm not getting acceptable groups I may put the Geissele on a carbine and pickup another BCM or something for this one.

_______________________________________________________________________________________________________________________________________________________

Thank you for contacting us and for your business. Also, thank you for being pro-active and sending those photos. This is normal with our barrel nuts and is perfectly acceptable. It should not have any bearing on accuracy.

Please let me know if I can be of further assistance.

Thank you,
Steve

 

[bigjake83]

Interesting reply from Geissele tech support about this issue. Apparently normal for their barrel nut...surprises me a little...

If I'm not getting acceptable groups I may put the Geissele on a carbine and pickup another BCM or something for this one.

_______________________________________________________________________________________________________________________________________________________

Thank you for contacting us and for your business. Also, thank you for being pro-active and sending those photos. This is normal with our barrel nuts and is perfectly acceptable. It should not have any bearing on accuracy.

Please let me know if I can be of further assistance.

Thank you,
Steve

I've installed a few Geissele handguards over the years and have never had the the gas tube pressing against the barrel nut

 

[Rerun7]

As long as the tube is aligned properly to the gas key will it have any effect on accuracy/reliability if it’s lightly resting on the barrel nut?

Doesn’t seem like it would be an issue but I haven’t run into this with any of my builds.

 

[WestDesertPRS]

I've installed a few Geissele handguards over the years and have never had the the gas tube pressing against the barrel nut

Yeah....it seemed odd to me as well. Its not "pressing" so much as resting against it. Not like it has to get forced into position or anything. I was more concerned about disruptive harmonics than anything.

 

[Rocketvapor]

Where is the contact ?
Does it touch towards the back at the receiver or just at the forward end where the tube bends?
If straight into the gas key sounds like tube bend adjustment.

 

[WestDesertPRS]

Where is the contact ?
Does it touch towards the back at the receiver or just at the forward end where the tube bends?
If straight into the gas key sounds like tube bend adjustment.

Pretty much light contact the whole length of the barrel nut. But according to Geissele tech support this is normal for their barrel nut and not a problem. I haven't installed a Geissele rail myself prior to this, so it was unexpected.

It's not pressing with any significant force, more like just resting. My biggest concern was setting up some kind of weird harmonic that will mess with accuracy.