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98Z5V

Gas tubes, barrel gas ports, and buffer weight

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This might end up as a long thread, but it shouldn't be too long.  It's a lecture, or a sermon, depending on how you look at it, and I'm not looking for feedback on what I'm about to say.  I'm publishing information.   In reality, it's pretty damned simple, but manufacturers are making it difficult for us.

Gas tube length is pretty much set, and it's standard - for the AR15 variants. The gas tube should END in the middle of the cam pin cutout, in the upper receiver.  Done.  That's it.  There's no more to the story, than that, and it's simple. THAT is "PROPER GAS TIMING" by design.  Anything short of that lessens your gas timing.  Anything beyond that increases your gas timing.  Period.

Your gas tube should look JUST like this, installed:

P1060637.JPG

^^^  That's a Rainier Arms Select barrel, .308 Win, midlength gas (true AR15 midlength gas tube) installed in an Aero Precision M5 upper receiver.  That is exactly right, and how it should be.

Now, I'm gonna break this down.  In a .308AR, you're almost always gonna see two gas systems - "Midlength" (which is completely fucked, by manufacturers), and Rifle length.  That's about all there is out there, for .308AR gas systems. 

We've run into this too many times to count, here.  TOO many times. Diagnosing problems, running conditions, whatever...  "My gun doesn't do (this)..."  :soap:

I delve into, this more often than not, right away, directly after I have to almost waterboard new people for their recoil system specs.  Recoil systems in the .308ARs is beyond fucked, and causes the majority of the problems in weapons operations, with gas systems being that "close second."  Gas port diameter in the barrel comes in at #3.  Those systems all need to be balanced, for proper weapons operation.  BALANCED.  It's three systems, or parts packages, but it all has to work together.  When ONE of them is completely fuckered, the gun doesn't run.  As it should...

I've preached extensively about carbine recoil systems in these things, and I'm not gonna beat it up again here.  I'll list that information in a later post, here.

There are TWO gas systems for .308ARs, in a nutshell.  "Midlength" and Rifle gas.  Things get complicated from here, though.  Let's start with Rifle gas.

Armalite developed this weapons platform, in it's entirety.  Completely, from soup-to-nuts.  They did it all, from it's base origin.  It started on 1 Oct 1954.

Armalite developed the AR-10 first.  They later developed the AR15 model.  Both original rifles were rifle length gas systems. the AR-10 Rifle length gas tube was 15.5".  When Armalite developed the AR15, the Rifle length gas tube was 15.25"...   I am not the designer, nor the engineer on these platforms.  I'm just delivering information.  Eugene Stoner was the designer, and he developed these two platforms in similarity, but independent of each other.  They share alot, but the differences cannot be overlooked.  Eugene Stoner had HIS REASONS for changing that gas system to a shorter length tube, when he went on to develope the AR15/M16, from his ORIGINAL design of the AR-10...  He's WAY smarter than me on that stuff, but that can't be ignored.  Many manufacturers these days are ignoring that, completely...

 

 

 

This thread right here gets CRAZY about differences in systems, so I'll post it now:

 

Edited by 98Z5V

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Gas tube lengths, courtesy of @survivalshop:

DPMS Gas Tube/AR 15/16

 

  Pistol             6-5/8

  Carbine          9-3/4

  Mid-Length  11-3/4

  Rifle             15-1/4

 

 

 

 

Armalite lengths,

 

Rifle ( 308 ) ----- 15.5 "

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"

AR15 National Match---------15 3/16"   (That's myinformation, from the one I have here...)

 

Edited by 98Z5V

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I recently bought a Wilson Combat .260 Remington barrel  - 2nd WC barrel I have.  It's the 20" Hunter barrel, rifle gas, and I should have learned from the first one, which was the .338 Federal 16" "midlength" gas barrel.

That 16" .338 Fed barrel was NOT "midlength."  It was in between AR15 midlength and AR-10 Carbine gas length - they drilled the fucker between those two 5.56mm/.308AR "standards."  They hope it will work, even if you fornicate up your gas tube selection, and get the wrong one.  I kid you not, and alot of barrel makers are doing this now. 

Here's the Wilson Combat 20" .260 Remington barrel - same exact shiit that I encountered on the 16" .338 Fed "midlength" gas barrel - which was not.  Wilson Combat is doing the "in-between" thing... You go short on your gas tube with AR15 gastubes, or you go a little long on your gastubes with real Armalite AR-10 gar tubes.  Short on the gas tube is not better.  You don't "meet the standard" and you don't get the minimum gas pressure that you need to cycle the weapons platform.  Your other choice, when manufactures do this bullshiit barrel drilling, is to "go long" on the gas tube...

That's FAR better for your gas timing, in the cycling of the weapons platform, than having it come up "short..."  try it out yourself, if you're a non-believer.  Your "functional problems" will end, when you get proper gas timing, from an appropriate gas tube length.

Here was my 20" .260 Rem Wilson Combat barrel, rifle gas system, with an AR15 Rifle gas tube:

P1060666.JPG

You just fucked me out of gas timing, Wilson Combat, with your "in-between" gas port bullshiit.  I'm short on power, because my gas key in my BCG is unlocking early, and the power to my gas key/BCG, isn't what was designed for this rifle. "It's only a little bit..." and "it'll still function with both gas tube lengths"...  is bulshiit.  Pick a design, and fucking stick with it, so people don't have to diagnose functional problems on the internet.

Pick a fucking standard.  ESTABLISH a fucking standard.  Armalite did it...  You "in-between" barrel manufacturers that think you're doing something smart - are actually fucking over customers.  "We'll just do ONE that's right on the middle, so it doesn't matter what gas tube they get!..."  YOU GUYS are the fucking problem here, because you can't get it right.  Eat a dick if you differ from my proof.  Choke on a bowl of smashed assholes, for desert, too.  Faxon - YOU guys went to this, based on some brainiac that thought it would be "better."  Fire that guy.

Get your shiit straight, barrel manufacturers.  Pick a design, STICK with your design and advertise it properly - if you can manage that.

We've never seen this here before, I know for a fact.  HERE is Armalite AR-10 Rifle gas tube versus AR15 Rifle gas tube:

 

 

P1060719.JPG

^^^  When looking at that pic above, "Height Over Bore" should scream out at people right away, in differences between "real" .308AR gas tubes, and AR15 parts...  It's pretty obvious...

Edited by 98Z5V

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Here's that Wilson Combat 20" Tactical Hunter barrel, drilled "in between" to appease customers... with a real Armalite AR-10 Rifle gas tube in it...

P1060720.thumb.JPG.e4d03cf012dd7900a664e7449654d5c6.JPG

The Wilson Combat .338 Federal barrel, 16", "midlength" gas was the same exact way. It wasn't "midlength" at all -it was Armalite AR-10 CARBINE gas length...

There's a MINIMUM standard here to meet, people, for gas system pressure, and gas system timing. When YOU FALL SHORT of that minimum gas system pressure and gas system timing - and your gun starts fucking up... WE hear about it,right here on this board.  Right here. Many times, it's like we, HERE, are to blame when we state what your problems really are.

It's not us  - we just point out what your malfunction is...  and the name calling starts, the bullshiit starts...   Whatever. 

I didn't design your cheap-ass weapons system. Nobody did, really - some upstart manufacturers designed your cheap parts, and I refuse to pay for them.  YOU, as the buyer did that, trying to build the cheapest .308AR you could.  "I WON!!! I built a $400 .308AR!!!!"

This isn't AR15-Land, with a real pattern to follow, and .308AR manufacturers do what they want. The end result of that BS in manufacturing lands right here on our laps, when we have to diagnose your failures to fire, failures to extract,failures to eject... and the magical "Double feed..."

PSA comes to mind, with all their fucking PA-10 Gen 1,Gen 2, Gen-whatever, problems that have rum AMOK on this board.  Yeah, since their beginning.

Fanbois - do your research.

 

Edited by 98Z5V

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This information on gas systems and gas port diameters shoe-horns directly into the other system that balances the gas system - the recoil system. Might as well throw this in here, and have a pretty complete thread of information on the two.  You can't have one without the other, and they must work very well with each other.  This comment in another thread is what lead to my posts on it:

 I noticed,  as a newcomer here the hubbub surrounding buffers and springs.

This piqued my interest - this statement right here, and got me thinking.

I had the M4A1 since it's introduction.  My first was #W318708.  That was the number of the gun on my weapons card, and the same one I had for 10 years. They had standard 3.250" AR15 carbine buffers in them, 3.0oz.  Not long after I got that gun, there was a "reliability improvement program" with them, and we had to send them all in to the "Depot Level Maintenance," which was our own armorers in that unit.  Some notification came down, guns were changed, and we hadn't even drawn them from the arms room to make that happen- our Armorer's made it happen.  Curious enough, those guys were right down the hallway from me, so I went in there to ask them what all the shiit was about.   "Ah, we put some new heavier buffer in there  had to take your buffer apart and take out a steel weight and put in a tungsten weight - one tungsten and two steel,  over the three steel weights, and we gave all you guys a new buffer spring..."  Fucking H1 buffer, at 3.8oz.

That was "necessary" to control the auto-fire in the 14.5" carbine-gas barrels, on the M4A1 - heavier buffer, new spring (stock spring).  We went from a 3.0oz standard buffer to a 3.8oz "H1" buffer - and they weren't marked - the unit armorers upgraded them with a tungsten weight in place of a steel weight...

Now,that made the M4A1 more reliable,in 5.56, in full auto.

How in the hell does that somehow come around to being "the ideal buffer weight" in a.308AR platform?  Short answer is, it's NOT. H1 buffer in a .308AR, that's designed for a 5.4oz buffer?!  Gotta be kidding me...  The .308AR platform was designed around a 5.4oz buffer, FIRST, in order to control the weight, mass and force of the BCG firing a .308 Win round through this platform.  Period. 

Part 2 coming up... 

--------------------------------------------------------------------------------------------------------------------

There's money involved around tungsten - alot of money.  You guys realize that when you pay for heavier buffers.  The more tungsten you buy (H1, H2,H3) the more you pay for it.  Go buy a VLTOR H6 buffer... You'll quickly see what I mean - 4 tungsten weights...  :laffs:

So, on a gun (Armalite AR-10) that was designed for a 5.4oz buffer, that was 5.200" long, running inside a receiver extension that was9 11/16" internal depth, ...   THAT was it's design, for proper operation. Done deal.  Period.

Armalite made a collapsible stock, and had to figure this out - they already knew that the buffer weight had to be 5.4oz, but the buffer had to be shorter, and so did the receiver extension.  Eugene Stoner developed a 7 5/8" internal depth receiver, because, BECAUSE, he changed the buffer to tungsten weights instead of steel, and got the buffer length down to 3.250" with those tungsten weights.  And the fucker weighed 5.4oz.  He made his design parameters WORK, based off the weight of the buffer that's required to run the AR-10 (the ONLY one running then...).

So, in short, the .308AR platform was already decided, WAY BEFORE US, and the minimum buffer weight needed was 5.4oz, and that was based on the rifle config.

Part 3 coming up.

-----------------------------------------------------------------------------------------------------------------------

So, you have a minimum buffer weight - something that's "enough ass to control the mass - and pressure."  How is it that DPMS did what THEY did on the LR-308?  They used an AR15 receiver extension that was 7.000" internal depth (they had them on the shelves, right?}.  They redesigned the buffer to work with a 7.000" internal depth collapsible extension (AR15 part), and came up with a 2.500" long buffer.  Even if you stuff an aluminum-bodied buffer with TWO tungsten weights, it only weighs 3.8oz.  You can't make an aluminum bodied buffer that's 2.500" long WORK in a collapsible extension on a .308AR, and make it any heavier than 3.8oz, even spending your money on those two (only two fit) tungsten weights... 

DPMS redesigned the spring.  They made it stiffer, in order to compensate.

No other manufacturer does this.  There are a shiit-ton of places that sell "Armalite AR-10 springs" and "DPMS LR-308" springs...  and don't have a clue.  Not one CLUE.  They just rebadge their AR15 springs.  And that don't cut it.

Everyone says, "The barrel, trigger and BCG are the heart of your accuracy..."

I won't argue that.

The recoil system and the gas system are the HEART of your reliability - and you MUST balance those two systems.

If you don't, your gun might be accurate - but it runs like shiit.

3.8oz buffers in a .308AR is not where you want to be.  Even if you get the perfect spring - you just compromised on the design of the system, from the very designer, Eugene Stoner.  You're making all kinds of other changes to make that gun run.  So far, I haven't seen anyone smarter than Eugene Stoner show up with anything else that's as reliable, in operation.  When you start "balancing compromises," which is both compromises in money and function, you compromised your reliability.

One perfect example I have is a specific manufacturer that likes to make cheap .308ARs, affordable to everyone, and with a "lifetime guarantee."  They ship with a gas port too small, and a gas tube that's too short - and they compensate for this with a recoil system that's too weak for the .308AR, .308Win round...  So, how does it work?  Typical complaints are, "It's over gassed, and I added an adjustable gas block to fix it..."

Yeah, so... How's it "over gassed" when the gas port is too small?  How's it over gassed when the gas tube is too short?  OH!  They used a recoil system toss-up with a buffer weight that was detemined "adequate" for the full-auto M4A1 5.56 rifle, some unknown spring, in a buffer that's 2.500" long, inside an AR15 Carbine receiver extension...  It's not "over gassed" in the least, and you DO NOT need an adjustable gas block to "tame that beast" at all.  You're under-recoiled from the get go, because that was CHEAPER to do on the assembly line, and other compromises were made in the barrel production, the serious compromise with gas port location on the barrel in order to use the cheaper - everywhere - AR15 gas tubes.  "Well, the gun SHOULD work most of the time, for most of the people, with most ammo...  "

Not good enough...

Off my :soap:

Edited by 98Z5V

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Placeholder 6

I want to tell you guys a story, about reciprocating mass...

The only reciprocating mass in your AR is the BCG weight and the buffer weight.  Your BCG isn't really your "recoil system," but you need to take it into account when you're putting your recoil system together. Lightweight BCGs and all that crap belongs in race guns.

I built this gun up from a new rail purchase, and a bunch of "stolen parts" from the first .308AR that I ever built.  Mk11 Mod 0.   Ish...

P1080374.JPG

I shot this gun two weekends in a row.  Two Sunday's ago, I took it out for it's "break-in," even though the barrel is from 2010, and is well broken in.  At 100 yards, re-zeroing the scope to this gun (stolen scope), at lower magnifications, it was fine.  Felt like any other .308AR, as far as recoil goes. Scope didn't jump off target, etc...   I immediately moved to the 475 yard target that I put out there, and cranked up the magnification.  At that mag power, and distance - the scope was jumping off target with every single shot.  I never saw any of my own hits...  I had to wait for my spotter to yell "HIT!" or not, then (on hits) I'd hear the impact a moment later.  Never got to see one of them...

So...  This original gun had a Tubb CWS in it (Carrier Weight System), with the tungsten insert.  Why NOT just put it back in here, since I'd already stolen so much from that gun?... So, I did. 

The CWS body with the tungsten weight in it comes in at 112 grams = 3.95oz.  I'm already running a 5.200" long .308AR rifle buffer that weighs 5.4oz.  Full size (not lightened) Fulton Armory chromed BCG that weighs 535 grams (18.87oz).  And I added 3.95oz directly into the back of the BCG, directly to the reciprocating weight of the entire recoil system...   That's a Quarter Pounder...  Is it exactly the same adding that weight to the BCG body, as it is to the buffer itself?  It damn near is, because it's reciprocating weight that runs the gun. Wouldn't really matter if you added it directly to the BCG, or to the buffer weight.

How did it affect the function of the gun? Took it back out there last Sunday.  Stupendous difference at 475 yards.  Scope never came off target once, and I watched every single hit that I made, and I saw the shots that I missed - and corrected my own misses for the follow-up shots - because I could SEE THEM now... 

5.4oz buffer + 3.95oz CWS = 9.35oz of reciprocating weight, which IS NOT counting my BCG weight - a full weight BCG...  

And some of these manufacturers think that a weakling 3.8oz buffer actually works in a .308AR?...   Rubbish...  Bullshiit.  3.8oz buffers don't beling in .308ARs, unless that's the "tuned weight" that you came up with in your Race Gun build. I've proven this time and time again. 

My $0.02.

Edited by 98Z5V

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98 ,You about sum it up as far as manufacturing spec's on 308AR's . I guess we could just purchase an complete factory Armalite AR 10 or DPMS LR 308's  & only use the factory components & parts & stick with one or the other platforms, but still some builders would still mix match parts & make them not function correctly .

It is that there is no manufacturing constancy for the various 308AR platforms, mostly the DPMS version  , Armalite & DPMS are the only ones that have a standardized platforms , its all the others that have made their own versions of these two that have muddied the waters, so to speak , with the retailers/Manufacturers calling everything AR 10 & it doesn't help & just confuses builders or those just plain acquiring replacement parts or components for an existing Rifle .

 The gas impulse needed for timing of a DI operated Action in the AR should follow the two Manufacturers mentioned above , one or the other , these manufacturers have spent a great deal of time & $$ in R&D to come up with a properly functioning system ( well the original Armalite did , the present company just bought the rights to someones else's work & design, which is OK  ) 

The Gas Tube length(s) are pretty much set in stone & then we have some that are made short or too long which only makes it worse to find the correct one , then the Barrel Manufacturers seem to have their own proprietary designs on where the Gas Port should be , as was posted by 98 , Then we have too small & too large Port sizes also to go with all the other BBL.issues .

I have a 20" Krieger/Criterion HB & its Gas Tube protrusion into the Upper Receiver is a little short  , but the rifle has functioned flawlessly from day one & is a tac driver , it could be the Gas Port size matches the gas impulse needed to make the system balance the way it was designed by DPMS , Rifle has DPMS Upper & Lower Receivers & DPMS BCG , AR 15 Rifle length Gas Tube . I say this because I no longer believe Gas Tube protrusions into Upper Receivers are a sure thing the set up will not work or work , as I used to believe . Its probably more of a combination of Gas Tube protrusion & the Barrels Gas Port size . Of course we are not talking about extreme lack of protrusion into the Receiver or for that matter too far of protrusion into the Upper Receiver. 

I have seen a DPMS Carbine gas system LR 308's that the GT Protrusion into the Upper was scary short & they have worked just fine , not how this may effect service life or performance , is another matter .

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I did that back in 2014, bought a new in the box DPMS Oracle LR 308, I have kept it in factory new unfired condition.  except for an aftermarket drop in trigger and mounted and boresighted scope. It is my go to for my personal LR308 standard DPMS rifle. Anyone can do the same for around $700,

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12 hours ago, survivalshop said:

98 ,You about sum it up as far as manufacturing spec's on 308AR's . I guess we could just purchase an complete factory Armalite AR 10 or DPMS LR 308's  & only use the factory components & parts & stick with one or the other platforms, but still some builders would still mix match parts & make them not function correctly .

It is that there is no manufacturing constancy for the various 308AR platforms, mostly the DPMS version  , Armalite & DPMS are the only ones that have a standardized platforms , its all the others that have made their own versions of these two that have muddied the waters, so to speak , with the retailers/Manufacturers calling everything AR 10 & it doesn't help & just confuses builders or those just plain acquiring replacement parts or components for an existing Rifle .

 The gas impulse needed for timing of a DI operated Action in the AR should follow the two Manufacturers mentioned above , one or the other , these manufacturers have spent a great deal of time & $$ in R&D to come up with a properly functioning system ( well the original Armalite did , the present company just bought the rights to someones else's work & design, which is OK  ) 

The Gas Tube length(s) are pretty much set in stone & then we have some that are made short or too long which only makes it worse to find the correct one , then the Barrel Manufacturers seem to have their own proprietary designs on where the Gas Port should be , as was posted by 98 , Then we have too small & too large Port sizes also to go with all the other BBL.issues .

I have a 20" Krieger/Criterion HB & its Gas Tube protrusion into the Upper Receiver is a little short  , but the rifle has functioned flawlessly from day one & is a tac driver , it could be the Gas Port size matches the gas impulse needed to make the system balance the way it was designed by DPMS , Rifle has DPMS Upper & Lower Receivers & DPMS BCG , AR 15 Rifle length Gas Tube . I say this because I no longer believe Gas Tube protrusions into Upper Receivers are a sure thing the set up will not work or work , as I used to believe . Its probably more of a combination of Gas Tube protrusion & the Barrels Gas Port size . Of course we are not talking about extreme lack of protrusion into the Receiver or for that matter too far of protrusion into the Upper Receiver. 

I have seen a DPMS Carbine gas system LR 308's that the GT Protrusion into the Upper was scary short & they have worked just fine , not how this may effect service life or performance , is another matter .

SS, you bring up very valid points.  Factory rifles generally work.  Generally.  There are a few that get out that don't run, from the solid manufacturers.  I'm only counting DPMS, Rock River,and Armalite in that group, too. Everyone else is "making a copy" and doing their own thing.  More often than not, it's these smaller companies that are jacking everything up. Lump aftermarket companies in there, too - there are companies that don't even produce firearms, and they make parts.

The fundamental misunderstanding of the platform, and it's major variations, is what gets people in trouble.  Aftermarket companies that don't understand a few key specs, AND terminology/nomenclature are the ones that are severely fucking this up.  Then, toss in the "junk companies" to the mix -  lowest cost, budget guns, from relatively unheard-of companies.  It's all off-shore produced, no QC, farmed out to the buyer at super-budget prices.  We've seen 'em.

Those buyers are usually the ones that come here and complain the most, when they're given decent information. They don't want to hear that they need to drill the gas port up, replace the gas tube, shiitcan the entire recoil system, and buy a decent BCG...   if their barrel isn't junk...  they blow up when they get given the honest information, and it's flame-on...  Budget prices will most usually attract "budget people" that think everything is under warranty forever, and it better last.  They need to go compare a Schmidt & Bender to their Tasco and tell me it's the same... 

The lack of a standard has fucked this platform, by the aftermarket. Some companies think they're gonna make the ONE PART that works on all three major flavors - and it never does.  There really are THREE major standards that can be followed, but the aftermarket (including barrel companies) don't follow any one of the three - they're trying to "combine" and save money... 

For recoil systems, there is ALWAYS HeavyBuffers.com. Clint is the man for recoil systems, and will get you straight, with the right parts.  Sprinco also has it down, and does just springs - that work. Knowing the differences between systems is what willhelp you select the correct parts for what you're building. 

Barrels, and this "in between" bullshiit for gas port location - whatever.  It's stupid.  It's better - FAR better - to go with the longer Armalite gas tube than a short AR15 gas tube, when you run into that situation.  Don't short yourself, and your rifle, by cutting your gas timing short.  It's far better to have a little more, than not enough.  That's the Demo Rule, right?  "When you think you have enough, add one more..." 

I'll keep going on this, and add to the placeholders I saved above.

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I just updated "Placeholder 6" above, and changed the title to reflect how far we've gone into buffer weights throughout this.

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