Gas Tubes

[98Z5V]

10 hours ago, Armed Eye Doc said:

I have heard and understand this.  But I think this is the most concise description of the interdependence of the two systems I have heard and thought it was worth highlighting so I can find it to share with others.

I'm chock full of all kinds of useless info, brother - you just have to feed me beer to get it out of me...  

[Armed Eye Doc]

15 minutes ago, 98Z5V said:

I'm chock full of all kinds of useless info, brother - you just have to feed me beer to get it out of me...  

You are how I know this information.  This was just extra concise.  This must have been during a low level of beer infusion. 

[98Z5V]

3 minutes ago, Armed Eye Doc said:

You are how I know this information.  This was just extra concise.  This must have been during a low level of beer infusion. 

Would have had to been the opposite of that, or you wouldn't have gotten it out of me...  

[Armed Eye Doc]

Just now, 98Z5V said:

Would have had to been the opposite of that, or you wouldn't have gotten it out of me...  

Well, it was late on a Friday night.  So I don't doubt it. 

[mrmackc]

I know this is an old thread, but I have been looking at gas tubes from several vendors and KAK in particular They show Rifle tubes Carbine tubes but they don't give the length. One vendor showed a gas tube for AR15, and LR308 to be 15.?? inches what is the correct length for a factory  barrel DPMS LR308 with a 16"barrel? Is there a gas tube chart and compatible buffer parts on this site? I couldn't find it but thought sometime in the past I saw one.

Thanks

 

As Gloria Radner would have said..."Oh,Well ...Never Mind"... I found Unforgivens post of:

DPMS LR 308 Gas Tube & /AR 15/16M4

  Pistol             6-5/8

  Carbine          9-3/4

  Mid-Length  11-3/4

  Rifle             15-1/4

Edited June 7, 2021 by mrmackc

[msgriff]

My current list:

GAS TUBE LENGTHS

AR15/DPMS LR308

• Olympic Arms Pistol 6-3/16"
• Pistol 6-5/8" - 6-3/4"
• Carbine 9-3/4" - 9-7/8"
• Mid-Length 11-3/4" - 11-7/8"
• Knight Armament SR-15 Mod 1 Mid-Length 13"
• Wilson Combat Match Grade Intermediate 13-1/4"
• Intermediate 13-3/4"
• Rifle 15-1/8" - 15-1/4"
• Rifle+2 17-1/8" (Adjust as required for +1, +3 etc.)

Armalite AR10

• Super SASS Carbine 11"
• Mid-Length Carbine 12-1/16"
• Rifle 15-1/2"

 

 

 

[crazyragincajun]

98Z5V & Others: I greatly appreciate the tech info in this forum. very good stuff i like digesting.

I bought a .308 BCA upper. (yes i know its considered cheap crap by some). I have some 5.56 stuff from them and was happy with it so i got it on sale and im going to try and make the best of it.

Since i know its a compromise using things like mil spec carbine tube length and short 2.5" buffer, I'm trying to make it closer to stoner's design characteristics.

Tore the upper down and this is what i have.

16" barrel. sold as a Mid Length, 0.086 gas hole.

BCG weighs 17.7oz

2.5" buffer weighs 3.8oz, but is solid inside. i watched high speed video of BCG bounce with solid buffers, so im going to make my own Carrier Weight System or drill out the buffer and put moveable tungsten in it, so it has the dead blow effect.

.308 specific spring for milspec carbine buffer tube.

Gas tube that came with it was 11 3/4 long tip to tip. center-ish of the gas hole is drilled 9.840 from front face of upper gas tube hole. this put the gas tube a little shallow in the upper, about 1/4 of the way into the cutout.

The gas tube has about .400 before it would bottom out in the BCG at installed location.

12.062" gas tube has been ordered.

adjustable gas block will be used.

I know the .308 has more recoil force on the case itself than 5.56, there was a test done where they connected two guns via gas tube. the gas only wouldnt really unlock and cycle the bolt of the other gun. therefore, i would suspect, less dwell time should work better than the 5.56 design parameters since it also has more gas volume, but a larger surface area to fill, so idk.

What i want to know is, has anyone put an intermediate or rifle length gas system on a .308 with a 16" barrel?

Am i wasting my time trying to plug the shorter location hole and drilling a new hole closer to the barrel end vs using the gas block adjustment?

does the AGB make the rifle more finicky with ammo/temp changes vs a shorter dwell time by reducing dwell distance/pressure by moving the gas sample 1.5" closer to the barrel, instead of 6.12" of dwell length, ~4.87" of dwell distance. what happens with .5" of dwell with a .308? would it cycle? does the gas tube ID become a restriction with that short of dwell?

The way i see it, the BCG/Buffer weight does two things. absorbs force & feeds the next round in. Obviously there needs to be a certain weight to strip rounds off in all conditions. I doubt theres much more force required to feed a .308 vs a 5.56 round from friction, distance, ect.

So that being said, recoil absorption without having a bolt speed too high or too low reward is the focus. 

 

[shooterrex]

Slow down. Just change 1 thing at a time. You ordered a longer gas tube. Good.

Your buffer even with tungsten will not be heavy enough unless the body is made of stainless steel.

Armalite sells the entire carbine recoil system for about $75.00.

This works. The recoil system also has to deal with the mass of the BCG going rearward not just feeding the next round.

Edited December 17, 2022 by shooterrex

[98Z5V]

^^^  Truth right there.  Heed those words.  

53 minutes ago, crazyragincajun said:

What i want to know is, has anyone put an intermediate or rifle length gas system on a .308 with a 16" barrel?

Yes.  Krieger/Criterion used to make a barrel specifically for Fulton Armory, 16" rifle gas.  0.936" gas block journal size with a 0.105" gas port diameter.  Flawless barrel, runs like a champ.  @DNPhas one of those barrels.   Criterion now makes a 16" rifle gas barrel with a 0.750" journal diameter, and I'm working with a guy right now to figure it out.  His gas port seems right, but time will tell.  

 

1 hour ago, crazyragincajun said:

16" barrel. sold as a Mid Length, 0.086 gas hole.

That gas port diameter works with 18" midlength gas barrels, but you're gonna need something at 0.090" or slightly larger for a 16" midlength gun.  Because of the shorter dwell time.  You won't need 0.095", but you'll need 0.090", maybe a touch more.  Positive on that.   <<<  That's with a proper recoil system, spring that's designed for a .308 and not AR15, and a buffer that weighs 5.4 oz or damn close.  

[crazyragincajun]

4 minutes ago, 98Z5V said:

^^^  Truth right there.  Heed those words.  

Yes.  Krieger/Criterion used to make a barrel specifically for Fulton Armory, 16" rifle gas.  0.936" gas block journal size with a 0.105" gas port diameter.  Flawless barrel, runs like a champ.  @DNPhas one of those barrels.   Criterion now makes a 16" rifle gas barrel with a 0.750" journal diameter, and I'm working with a guy right now to figure it out.  His gas port seems right, but time will tell.  

 

That gas port diameter works with 18" midlength gas barrels, but you're gonna need something at 0.090" or slightly larger for a 16" midlength gun.  Because of the shorter dwell time.  You won't need 0.095", but you'll need 0.090", maybe a touch more.  Positive on that.   <<<  That's with a proper recoil system, spring that's designed for a .308 and not AR15, and a buffer that weighs 5.4 oz or damn close.  

Cool. I might try as is since my buffer is lighter than that and see what happens. While i was paying freight i got a 308 rifle buffer system anyway, just incase the short buffer ends up being problematic.

I also may end up leaving it as a straight pull bolt action by turning the gas off. Its a side charger, so easy peasy for that.

Options, they are nice if they work lol

 

Thanks for the gas info!

[98Z5V]

Plugging your midlength gas port and drilling another at rifle or intermediate length will not be realistic.  Your gas journal diameter is 0.750, but it probable tapers or steps down to 0.740" after that journal area.  Finding a gas block for a 0.740" barrel won't be possible.

All this intermediate length gas is a new thing, mainly coming from Wilson Combat.  It works, if done properly.  It's not at all common, though.  

White Oak Armament will make you a proper gas tube, in any length that you tell them.  

[crazyragincajun]

2 minutes ago, 98Z5V said:

Plugging your midlength gas port and drilling another at rifle or intermediate length will not be realistic.  Your gas journal diameter is 0.750, but it probable tapers or steps down to 0.740" after that journal area.  Finding a gas block for a 0.740" barrel won't be possible.

All this intermediate length gas is a new thing, mainly coming from Wilson Combat.  It works, if done properly.  It's not at all common, though.  

White Oak Armament will make you a proper gas tube, in any length that you tell them.  

Good point. Ill have to measure the barrel. While i just had a lathe and mill delivered today, its going to be a bit before i can use them.

I doesnt sound like a longer gas system is worth testing on 16".

[98Z5V]

6 minutes ago, crazyragincajun said:

I doesnt sound like a longer gas system is worth testing on 16".

It's not - 16" midlength will run great, once you get everything sorted.  It'll be a soft shooter, as much as a .308 Win gasser can be.  

I have a 13.5" midlength that runs like a dream.   

Edited December 18, 2022 by 98Z5V

[crazyragincajun]

Finally got the longer gas tube in.

I bought a rifle length 308 buffer setup too just to make sure i can have a reliable rifle.

3d printed a sleeve to use a mil spec stock on the rifle buffer 😉

[GStephen]

On 7/7/2019 at 2:02 AM, Lr-308FUn said:

It's a mid-lenght gas on that 16" barrel. Now would a Armalite AR-10 Carbine gas tube be long enough, also where to get one? I have looked, most are out of stock. It has a .750" diameter gas block by Aero. I got a Aero M5 lower parts kit https://www.primaryarms.com/APRH100158 

Now if getting a Armalite Carbine gas tube, would that help with recoil management a bit? It has a kick, a bit more than most have had. 

Thanks for the information. 

I just got 2 of the 12.0625” gas tubes from armalite.com. They were in stock.

  Lol. Didn’t read the date of the post I replied to.  

Edited December 29, 2022 by GStephen

[98Z5V]

6 hours ago, crazyragincajun said:

Finally got the longer gas tube in.

I bought a rifle length 308 buffer setup too just to make sure i can have a reliable rifle.

3d printed a sleeve to use a mil spec stock on the rifle buffer 😉

Yep, that's damn near perfect, and much more gooder than a shortass gas tube, cheating you out of some important gas timing.  Very nice.

But, no pic of this 3d printed sleeve?   Come on, Man!   

[crazyragincajun]

[98Z5V]

SWEET!!!   

[NightStalker]

I had read the same thing about getting an Armalite gas tube so I tracked down one that measured 121/8. The day I assembled my upper it came time to install the BCG and noticed it wouldn’t slide all the way in. Then realized the gas tube was extending past the can pin cut out requiring a shorter gas tube. 
a quick swap with an 113/4 gas tube and it runs great. 
The pic shows the one that to long. 
The tube should be about center of the notch but if yours runs and it’s good for you run it. 

[shooterrex]

It all depends on where the barrel maker drills the gas port.

[98Z5V]

5 hours ago, NightStalker said:

I had read the same thing about getting an Armalite gas tube so I tracked down one that measured 121/8.

That's not an Armalite AR-10 rifle gas tube.  They measure 12 1/16", not 12 1/8".  It's obvious that your gas tube is too long, so in light of that, who did you order this gas tube from (what vendor), and what's the brand of it - the manufacturer's name?  <<  That's important information, for the future, for everyone on this message board.

4 hours ago, shooterrex said:

It all depends on where the barrel maker drills the gas port.

^^^  This right here is equally important.  What brand is your barrel, and what vendor did you get it from? 

Without that information, we really can't help much. 

[NightStalker]

On 1/30/2023 at 10:11 PM, 98Z5V said:

That's not an Armalite AR-10 rifle gas tube.  They measure 12 1/16", not 12 1/8".  It's obvious that your gas tube is too long, so in light of that, who did you order this gas tube from (what vendor), and what's the brand of it - the manufacturer's name?  <<  That's important information, for the future, for everyone on this message board.

^^^  This right here is equally important.  What brand is your barrel, and what vendor did you get it from? 

Without that information, we really can't help much. 

I posted all the info in a post called gas block. I’ll try to find it