Where do you measure a LR308 barrel to determine gas system length?

[Dev L]

I have a Wilson Combat 6.5 Creedmoor barrel I highly suspect is 3/16" longer than AR15 rifle gas length and 3/16" of an inch shorter than AR10 rifle gas.

I assume I measure from tbe center of the gas port to where exactly? And what should that measurement be for a LR308 barrel for each gas system length?

Just want correct figures before deciding what to do with this barrel.

As a bonus, do different recievers locate the barrel at different depths or do various carriers have different gas key locations or lengths?

 

[_Windrider_]

 

[rpoL98]

just keep in mind, for DPMS-pattern large-frame uppers, there's two different gas-system lengths in play. Probably the most common is the DPMS LR-308 "standard" which uses the common AR-15 gas tube lengths.

The other "standard" is the Armalite AR-10 gas-system length, which is also applied to DPMS-pattern large-frame uppers (and associated barrels). The Armalite AR-10 gas tubes are about 3/8" longer than their AR-15 counterparts, and to further muddy the waters, the Armalite AR-10 carbine gas tube is about ~3/8" longer than the AR-15 mid-length gas tube.

from my own approximate measurements, the AR-15 rifle-length gas tube is about 15-1/8", the Armalite AR-10 rifle-length gas tube is about 15-1/2" OAL.

the AR-15 mid-length gas tube being about 11-3/4" long, and the Armalite AR-10 carbine gas tube being about 12-1/16" long.

Again, these are my own observed measurements from my own samples, whether those are the absolute standard spec dimension, I have no idea, but this is what's worked for me over the years now.

I know Faxon uses the Armalite AR-10 standard for their DPMS-pattern 308 & 6.5CM barrels, and I suspect Wilson does also, judging from forum chatter, although I've never owned a Wilson large-frame AR barrel myself.

YMMV.

AR-15 gas tube when an Armalite AR-10 gas tube should've been used, instead. Subsequently replaced.

 

[Dev L]

I am well aware of the different gas tube lengths and those stats are easy to find.

I presume the gas system diagrams show AR15 gas system lengths correct?

Per the response with gas tube termination relative to the cam pin cutout... I am using the 2A Xanthos upper. The cut out for the cam pin is squared off, not a semi circle. I assume it is located at the same point as other semi circular cam pin cut outs. An AR15 rifle gas tube looks longer than the first pic, but shorter than the second. Thus my concern over this barrel possibly being between the two standards.

 

[msgriff]

Measure from the end of the barrel extension to the center of the gas port. Add ~1" for the portion of the gas tube which extends into the upper, as shown in the image below. Then for gas tubes manufactured to mil-spec, add 0.605", which is the dimension from the center of the gas opening on the bottom of the gas tube ( which is in line with the center of the gas port) to the end of the gas tube.

ETA: Another way to put it is to measure from the end of the barrel extension to the shoulder of the gas journal and add ~1.9".

 

[Evintos]

Wilson Combat uses the AR10 rifle length (15.5")for their large bore AR10 builds and barrels (unless it's their shorter 16" barrel in which case they use intermediate length 13.25" gas tube). If the gas tube is short but not too short, it can still function if BCG goes into battery and there is gas tube to gas key engagement. However, you may run into short stroke issues (under gassed) depending on ammo, reciprocating mass, gas port diameter, etc.

Pic below of what an AR15 rifle length gas tube looks like in a 2A Xanthos.

As a bonus, do different recievers locate the barrel at different depths or do various carriers have different gas key locations or lengths?

While it won't vary too much (subjective measure), the answer is yes; whether it's the result of design or tolerance stacking.

 

[rpoL98]

Wilson Combat uses the AR10 rifle length (15.5")for their large bore AR10 builds and barrels (unless it's their shorter 16" barrel in which case they use intermediate length 13.25" gas tube). If the gas tube is short but not too short, it can still function if BCG goes into battery and there is gas tube to gas key engagement. However, you may run into short stroke issues (under gassed) depending on ammo, reciprocating mass, gas port diameter, etc.

Pic below of what an AR15 rifle length gas tube looks like in a 2A Xanthos.

[sorry, can't see the pic, insert Stevie Wonder "Ican't see shit" meme]

While it won't vary too much (subjective measure), the answer is yes; whether it's the result of design or tolerance stacking.

can't see the google pic.

 

[Evintos]

can't see the google pic.

Whoops, should be fixed.

 

[Dev L]

My gas system from front of receiver to back of gas block is 12.925" best I can measure. With a new AR10 15.5" gas tube from Wilson Combat, my gas tube protrudes 1.1" to 1.125" into the receiver.

It certainly seems I have a gas system about 0.1" shorter than true AR10 length. This is causing my gas tube to extend 0.1" further into the upper than it should.

Currently, my AR15 rifle length tube short strokes, but the AR10 tube is bottoming out in my JP bolt carrier by just the tinniest amount.

Soooo is this a common issue with Wilson Combat? Is there anything I can do besides trying to get a new barrel?

 

[msgriff]

My gas system from front of receiver to back of gas block is 12.925" best I can measure. With a new AR10 15.5" gas tube from Wilson Combat, my gas tube protrudes 1.1" to 1.125" into the receiver.

It certainly seems I have a gas system about 0.1" shorter than true AR10 length. This is causing my gas tube to extend 0.1" further into the upper than it should.

Currently, my AR15 rifle length tube short strokes, but the AR10 tube is bottoming out in my JP bolt carrier by just the tinniest amount.

Soooo is this a common issue with Wilson Combat? Is there anything I can do besides trying to get a new barrel?

White Oak Armament makes custom length gas tubes, but before I spent that kind of money on a gas tube, I'd be looking at other solutions. It might be resolved by simply opening up the gas port and using the AR-15/DPMS length tube, but I would check out a number of other things first. There are a few different issues possible, such as the wrong length buffer for the RE.