Gas Tubes

[Lr-308FUn]

I got this Aero M5 build with a BCA 16" mid-length gas system DPMS profile. I have had no issues with it firing got about 340+ rounds through it without a issue. I have read that I could need a Armalite mid-length gas tube instead of a DPMS length. I know it looks a bit short, but works fine. So leave it or go with a Armalite tube. 

 

[unforgiven]

So if it runs run it...

[Lr-308FUn]

Indeed 

 

[98Z5V]

The gas tube should end in the center of the cam pin cutout, by design, in order to have the appropriate amount of gas timing before the BCG separates itself from the gas source.

I'd get that thing out of there and get an Armalite AR-10 Carbine Gas Tube in it.

So, if you're cool with the function of it... - what's your recoil system look like? 3.8oz buffer that's 2.5" long, some weird spring, 7" internal depth extension?  Know the gas port diameter in the barrel.  18" barrel midlength gas, 0.750 gas block diameter should be 0.080~0.085" gas port diameter.  I imagine you'd need 0.085~0.090" gas port diameter to compensate the the shorter dwell time of the 16" barrel over an 18" barrel.

There's a series of engineered or accidental "compromises" going on there, just to make the rifle function - but if you're happy with the function, then that's all that matters. 

Edited July 6, 2019 by 98Z5V

[Lr-308FUn]

On 7/6/2019 at 12:46 AM, 98Z5V said:

The gas tube should end in the center of the cam pin cutout, by design, in order to have the appropriate amount of gas timing before the BCG separates itself from the gas source.

I'd get that thing out of there and get an Armalite AR-10 Carbine Gas Tube in it.

So, if you're cool with the function of it... - what's your recoil system look like? 3.8oz buffer that's 2.5" long, some weird spring, 7" internal depth extension?  Know the gas port diameter in the barrel.  18" barrel midlength gas, 0.750 gas block diameter should be 0.080~0.085" gas port diameter.  I imagine you'd need 0.085~0.090" gas port diameter to compensate the the shorter dwell time of the 16" barrel over an 18" barrel.

There's a series of engineered or accidental "compromises" going on there, just to make the rifle function - but if you're happy with the function, then that's all that matters. 

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. 

[98Z5V]

35 minutes ago, Lr-308FUn said:

 

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. 

 

You still didn't answer my recoil system questions that I asked you, but I'l tell you right now that is has more kick because you're "under-recoiled."

Excuse me for asking meanass questions - most people feel "attacked" when I start asking questions, and quickly go "full-on defensive" about it, like I'm trying to insult their intelligence or something.  But I'm gonna ask some questions, here.  I mean no harm.

"More than most you've had" means what?  Other .308ARs?  Other 5.56 guns?  Bolt guns? 

It probably "has a kick, a bit more than most you've had" because it's a giant compromise in the two major systems that run the gun, and that's just to get it to work.  There was a giant "money" compromise in the recoil system, AND the gas system - or a total lack of understanding on the manufacturers part, in it's design.  That "money" compromise was aluminum vs. stainless steel in the construction of the buffer body, plus the cost of tungsten.  The other compromise was in the spring - SO EASY to use an AR15 spring, or something generic - and not .308AR specific. So, there's a giant compromise in the recoil system - and how do you beat that, as a manufacturer? 

AR15 gas tubes are made from everyone - so let's just use those.  Dime a dozen.  The current "inexpensive" barrel-manufacturer route in the last couple years is to just drill a gas port location somewhere "between" the DPMS LR-308 gas port location, and the Armalite AR-10 location - somewhere "in between" - and then our customers can use ANY gas tube and it'll work.  Another compromise in the system.  And it doesn't always work.

So, we're at a weak recoil system, and a gas tube that isn't at spec - what do we do to get the gun to run on .308 Win ammo now?  Change the gas port diameter, go smaller.

What you're getting into when you take on these kinds of things is "race gun shiit."  You start dabbling around in lighter buffers, weaker recoil springs, smaller gas port diameters,  - that's "race gun territory" right there.  Might as well just toss in a lighter BCG while you're at it.  Throw race gun parts at it. 

That does NOT make a functional factory rifle.  Most of these "factories" do not understand that, and they make up a bunch of parts that "They" think will work, combine AR15 parts that are not up to spec on the larger ARs, and just say, "eh, it'll work for most of the people, most of the time, with most of the ammo..."

If you're in that crowd, and your gun works - then don't change the ammo that you're using.  You can build the gun right, so it'll function all the time - or you can take what you've got, with all it's compromises - and don't ever change the ammo you're using.  Don't expect the same results from your gun if you change ammo.

Edited July 7, 2019 by 98Z5V

[MikedaddyH]

Your gas port diameter ?????

Length of recoil spring , count coils ????  ?????

Length of gas tube  .????

Size of buffer (length) & (weight) ????  ????

Weight of BCG  ??????

[survivalshop]

I have seen quite a few 308 AR's with the Gas Tube positioned like that & they worked fine , but they were Carbine Gas Systems .Kinda makes you wonder what size Gas Port your Barrel has.

 

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

 

 

 

 

Armalite lengths,

Rifle ( 308 ) ----- 15.5 "

Mid length Carbine ( 308 )--12 1/16"

super SASS Carbine ( 308 )--11"

Super SASS< Rife (308 )   ?

Mid ,( 223 )------------------ 11 3/4"

Carbine ( 223) --------------- 9 3/4 "

Rifle ( 223 ) ------------------- 15 3/16"

 National Match---------------  ?

[Lr-308FUn]

13 hours ago, 98Z5V said:

You still didn't answer my recoil system questions that I asked you, but I'l tell you right now that is has more kick because you're "under-recoiled."

Excuse me for asking meanass questions - most people feel "attacked" when I start asking questions, and quickly go "full-on defensive" about it, like I'm trying to insult their intelligence or something.  But I'm gonna ask some questions, here.  I mean no harm.

"More than most you've had" means what?  Other .308ARs?  Other 5.56 guns?  Bolt guns? 

It probably "has a kick, a bit more than most you've had" because it's a giant compromise in the two major systems that run the gun, and that's just to get it to work.  There was a giant "money" compromise in the recoil system, AND the gas system - or a total lack of understanding on the manufacturers part, in it's design.  That "money" compromise was aluminum vs. stainless steel in the construction of the buffer body, plus the cost of tungsten.  The other compromise was in the spring - SO EASY to use an AR15 spring, or something generic - and not .308AR specific. So, there's a giant compromise in the recoil system - and how do you beat that, as a manufacturer? 

AR15 gas tubes are made from everyone - so let's just use those.  Dime a dozen.  The current "inexpensive" barrel-manufacturer route in the last couple years is to just drill a gas port location somewhere "between" the DPMS LR-308 gas port location, and the Armalite AR-10 location - somewhere "in between" - and then our customers can use ANY gas tube and it'll work.  Another compromise in the system.  And it doesn't always work.

So, we're at a weak recoil system, and a gas tube that isn't at spec - what do we do to get the gun to run on .308 Win ammo now?  Change the gas port diameter, go smaller.

What you're getting into when you take on these kinds of things is "race gun shiit."  You start dabbling around in lighter buffers, weaker recoil springs, smaller gas port diameters,  - that's "race gun territory" right there.  Might as well just toss in a lighter BCG while you're at it.  Throw race gun parts at it. 

That does NOT make a functional factory rifle.  Most of these "factories" do not understand that, and they make up a bunch of parts that "They" think will work, combine AR15 parts that are not up to spec on the larger ARs, and just say, "eh, it'll work for most of the people, most of the time, with most of the ammo..."

If you're in that crowd, and your gun works - then don't change the ammo that you're using.  You can build the gun right, so it'll function all the time - or you can take what you've got, with all it's compromises - and don't ever change the ammo you're using.  Don't expect the same results from your gun if you change ammo.

 

7 hours ago, MikedaddyH said:

Your gas port diameter ?????

Length of recoil spring , count coils ????  ?????

Length of gas tube  .????

Size of buffer (length) & (weight) ????  ????

Weight of BCG  ??????

Here is the Buffer kit I used, again I used a Aero Precision M5 buffer kit. I counted the coils on the buffer spring 27, it's 11" long. 

Now the barrel is this barrel (see pics) 

I did just notice it says AR-10 which is Armalite profile barrel. I didn't see it state anywhere on their being DPMS profile on that barrel. I did purchase it on Primary Arms website 

At this time yes the rifle functions but I want to make sure that it is correctly assembled. I wasn't sure about that barrel when I purchased it, I did because I was really trying to build a functioning AR-10/Lr-308 rifle under $1,000 dollars. I won the bet & made myself $50 bucks. 

I hope this information helps. Also the ejection pattern on all ammo used is at a good 3'O'clock ejection pattern. Now would a Armalite profile barrel even fit in a DPMS profile upper like the Aero Precision M5 upper? 

Don't worry you won't offend me, I like it when I get replies back with a down right honest answer. I just don't want this rifle tearing itself up by using incorrect parts. Thanks. 

 

 

 

 

 

[MikedaddyH]

Everything seems right ,but not sure about the gas tube with your barrel . It does NOT appear to be long enough.

[Lr-308FUn]

That's what I've been asking. Now what kind to get, I am not tearing apart the barrel again to measure the gas port length again. It cycles fine just want the correct parts if not using the correct parts. So where can I find a Armalite gas tube. Been looking everywhere. Also which one to get Carbine or mid-length Armaliet tube. The barrel I have is a Mid-length gas. 

This is the length of the tubes I've been using, 11 3/4" tubes. Now do I need the Armalite 12" or 12 1/16" Thanks

[98Z5V]

On 7/7/2019 at 2:27 PM, Lr-308FUn said:

I hope this information helps. Also the ejection pattern on all ammo used is at a good 3'O'clock ejection pattern. Now would a Armalite profile barrel even fit in a DPMS profile upper like the Aero Precision M5 upper?

I've got a complete, badass little .308 rifle that is Aero Precision upper, lower and rail.  All other operational parts are Armalite AR-10 (barrel, gas system, BCG, recoil system), straight from Armalite themselves.  It runs like a champ. 

It's completely possible, and it works well in that configuration. 

[98Z5V]

On 7/7/2019 at 2:37 PM, Lr-308FUn said:

That's what I've been asking. Now what kind to get, I am not tearing apart the barrel again to measure the gas port length again. It cycles fine just want the correct parts if not using the correct parts. So where can I find a Armalite gas tube. Been looking everywhere. Also which one to get Carbine or mid-length Armaliet tube. The barrel I have is a Mid-length gas. 

This is the length of the tubes I've been using, 11 3/4" tubes. Now do I need the Armalite 12" or 12 1/16" Thanks

Armalite only makes two gas tubes for their AR-10, Carbine and Rifle gas tubes.  Their Carbine gas tube is 12 1/16" long. That's the one you need.  There are 18 of them in stock at Armalite right now, as I type this:

https://www.armalite.com/product/ar-10-carbine-length-gas-tube-10007005/

[98Z5V]

That recoil system you linked - is just like all the other DPMS-based recoil systems out there.   There's room for improvement in it, and at the bare minimum, I'd replace the recoil spring with the Sprinco Orange spring, if it were my own setup. 

[Lr-308FUn]

Well I did it, finally got the Armalite AR10 carbine tube installed, It does look much better. Looks like where it should be. Now will that help with recoil, not that I worry about recoil. I also have a Helius Tactical 1776 black brake coming. Cannot wait to get it had great reviews on their website. 

 

Now just need that muzzle brake & it will be done. Also does anyone have any experience with JP Enterprise's one piece gas ring for the Bolt. The original would fall on it's own weight, I guess its the same as Ar15 bolts they have to hold up to their weight. Well the JP one doesn't, I states that it won't. I have about 300+ rounds through it already but wasn't sure why it was killin gas rings. Thanks. Please let me know where to get some good to go gas rings. 

[jtallen83]

44 minutes ago, Lr-308FUn said:

Also does anyone have any experience with JP Enterprise's one piece gas ring for the Bolt. The original would fall on it's own weight, I guess its the same as Ar15 bolts they have to hold up to their weight. Well the JP one doesn't, I states that it won't. I have about 300+ rounds through it already but wasn't sure why it was killin gas rings.

Many manufacturers are touting this loose feature as a way to ease over-gassing on 308 AR's. My AR-10 McFarland rings have always been tight;

https://www.armalite.com/product/ea1055-ar10-mcfarland-gas-ring/

[Lr-308FUn]

Now will these work on a DPMS pattern BCG? Thanks for the link

[jtallen83]

3 hours ago, Lr-308FUn said:

Now will these work on a DPMS pattern BCG? Thanks for the link

I can’t remember if I have used one on a DPMS pattern bolt. I can give it a try when I get home in a week or so.

[Lr-308FUn]

Thanks 

 

[98Z5V]

4 hours ago, jtallen83 said:

Many manufacturers are touting this loose feature as a way to ease over-gassing on 308 AR's.

I love that statement. The over-gassed ones they're talking about probably aren't over-gassed at all - more than likely, they're under-recoiled...

@Lr-308FUn, your new gas tube came out perfect - right on the money, dead center of the cam pin cutout.  

[Blewbyu]

Ok I am going to do mine now. 

[hiprimer]

Not to hijack but.... when I installed my BA 20" barrel I had to go back to the AR15 length gas tube.   BA positioned the port closer to the breach so the AR15 gas tubes would fit.   Is this relocation of the port a good idea?  Rifle seems to function just fine but I do have the Armalite AR10 spring and a heavy rifle buffer (over 8 oz) installed.

[98Z5V]

10 hours ago, hiprimer said:

Not to hijack but.... when I installed my BA 20" barrel I had to go back to the AR15 length gas tube.   BA positioned the port closer to the breach so the AR15 gas tubes would fit.   Is this relocation of the port a good idea?  Rifle seems to function just fine but I do have the Armalite AR10 spring and a heavy rifle buffer (over 8 oz) installed.

Install which ever gas tube that ends at the center of the cam pin cutout in the upper receiver.

I'm hoping this "hybrid gas port location" shiit fades away.  It's a very stupid idea, on the part of manufacturers.  It's fucking ignorant. 

Your recoil system doesn't have anything to do with what your gas system is.  I.E., you don't have to run a Rifle Recoil System if you have a Rifle Length Gas System. Your gas system AND your recoil system have to be balanced, and work together.  Your recoil system has to control the weight of your BCG, and the force of the recoil of your round.  Your gas ssytem has to deliver enough force/power to cycle the action.  Hope that makes sense. 

[Armed Eye Doc]

10 hours ago, 98Z5V said:

Your recoil system doesn't have anything to do with what your gas system is.  I.E., you don't have to run a Rifle Recoil System if you have a Rifle Length Gas System. Your gas system AND your recoil system have to be balanced, and work together.  Your recoil system has to control the weight of your BCG, and the force of the recoil of your round.  Your gas ssytem has to deliver enough force/power to cycle the action.  Hope that makes sense. 

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.

[Blewbyu]

Ok I am going to do mine now. Just called and talked to Greg and purchased a carbine gas tube and ar10 bolt catch. Man Aramalite has great customer service!!!!!! I am a customer for life. Thx