AR-10 vs. DPMS Gas Tubes - FTF issue

[Lancer1]

Dang, I'm having a heck of a time trying to resolve this.  I received a gas tube advertised with the correct part number (10007010) from a place called Delta 3, but it is not 15 - 1/2" long.  The technicians at ArmaLite have confirmed that the actual ArmaLite AR 10 gas tube is indeed 15 - 1/2".  Delta 3 must have sent me the M-15 gas tube which is 15 - 3/16", so it is not long enough.  ArmaLite took my order for the original, but it is back ordered with the arrival being unknown.  This sticking point has brought me to a halt with my 22" Fulton Armory built rifle.  "The Devil is in the Details"!  Fortunately I have another complete rifle that works like it should, and I just put a Timney trigger in there.  It has an 18" barrel, and shoots really straight.  But I really wanted to blast that 22" stainless barrel this week.  I just have to be patient, and wait!

[Lancer1]

My 308 build problem has come to be resolved.  I installed the actual ArmaLite 308 gas tube which is actually 15 -1/2" long.  I installed an upgrade to the extractor from Fulton Armory, along with the stiffer extractor spring (5 coil), the poly insert, and the rubber O ring.  I installed the Timney 4 LB trigger, and a JP adjustable gas block.  I replaced the weeping DPMS magazines with KAC 10 round mags.  This rifle has been a great learning experience for me.  I built it from an assemblage of parts, and you really have to fine tune it to get it working properly.  This thing functions flawlessly, and is deadly accurate.  No more stove pipe / feeding / ejection issues.  The gas tube now reaches all the way into the bolt carrier key, and imparts a full gas charge.  The new magazines feed correctly.  The Fulton Armory 22" Stainless Bull barrel is an absolute tack driver.  Even though this California legal rifle is impaired with the required bullet button, it is now a trusted, and favorite gun.  Thanks to all for the inputs and discussion.  The internet and 308AR.com are wonderful things!

[98Z5V]

That's great news, Lancer - great work.  <thumbsup>

[washguy]

Wooo hooo great work there :) Wash

Edited October 2, 2013 by washguy

[unforgiven]

Congrats brother Lancer.

[Wraith1967]

I found and ordered an AR-10 Gas Tube for $12.  What is interesting is that Fulton Armory's barrel (gas block shoulder) is 3/8" farther down the barrel than many other DPMS products.  I have read so many accounts of feeding problems, with many possible causes.  There are really hundreds of theories as to why these guns don't feed correctly.  However, when doing a build yourself, you really have to look very precisely at the fitment of ALL of the parts.  You can't just assume each and every part will fit and function properly (from many different vendors), just because it is advertised as DPMS compatible.  Take the magazines, I have two actual DPMS mags that don't work.  I can clearly see that the primers of inserted rounds are lower than rounds placed in an after market mag (the lips have different angles).  The after market mag feeds correctly, the DPMS mags don't.  I have now ordered 4 different mags (from different manufacturers) searching for the best feeding mag.  I ordered two KAC mags, and they were $125 each. I notice that they are welded, not just bend (press) formed, so I'm assuming that's why they are so expensive.  Availability is scarce, but after much "googling", I have found; PMAGS, DPMS, KAC, PRO-Mag, and ASC.  I have not received all of them yet, so I can't testify as to the function of each of them.  I read one account of a fellow who purchased a completed DPMS factory LR-308 ($5500), and he has expierenced much feeding problems (he sent it back to DPMS twice, still does not work).  Other guys swear by their DPMS rifles, with no hitches whatsoever.  One theory that seems to make sense is the quality control has suffered, to meet the demands of the purchase frenzy.

 

 

 Where did you get the gas tube for your DPMS 308. I need one. Thanks

[Robocop1051]

Where did you get the gas tube for your DPMS 308. I need one. Thanks

LR308 uses a standard AR gas tube. For that matter, so does the AR10 (Car and Mid)... except for the AR10 rifle length

[Lancer1]

Robocop1051, I got my (authentic ArmaLite Rifle length gas tube - 15-1/2 inches long) from a website called DSG Arms.  They have the real mcoy, and I also got one from Armalite itself.  I bought one from a place called Delta 3 tacticle (advertised as an ArmaLity part), but it was not a real ArmaLite rifle length gas tube, as it was only 15 - 3/8, which is a standard AR 15 rifle length.  That one was no good to me, and I complained to Delta 3, but they would not respond.  Anyway, the actual, no-S#@% Armalite tube is what I needed, and now my rifle works like it is supposed to.

[Lancer1]

OK, I meant that for Wraith 1967, not Robocop.  With regard to Robocop's statement, the real ArmaLite AR-10 rifle (rifle length gas system) uses a 15-1/2" long gas tube.  This is right from the ArmaLite technichians from their factory.  The DPMS platform can use any AR 15 type gas tube - 15-3/8" long. (Rifle Length gas tube system).  My LR 308 clone that I built with a Fulton Armory barrel, had to have the actual ArmaLite gas tube, as the AR 15 gas tube would not reach far enough into the upper receiver to engage the gas key.  So, for Wraith 1967, I got my 15-1/2" gas tube from DSG arms.

[dingdong]

I've been having the same problem (short-stroke/short tube) with my Fulton FAR308 upper and all the posts here have been very helpful.  So thank you all for the lively and active discussion. 

 

The other reason I'm chiming in is because I've also been looking for an AR10 gas tube, and I've also come across Delta3tactical.com as a resource for AR10 parts.  After reading this forum post I sent Delta3 an email asking them if they resolved the tube length problem and got a phone call (no kidding) two minutes later. The caller explained that they erroneously sent you the wrong tube and apologized to me (for some reason) for the mix up.  He said he had the AR10 tube in front of him (while we talking on the phone) with a ruler and it was exactly 15-1/2".

 

I'll chime back in when I get my tube and either verify or neigh-say this as a fix for Fulton FAR308 rifles with incorrect gas tubes, barrels, or what ever is going on that is making the guns short-stroke (I've ruled out the buffer, springs, mags, & ammo.  If this doesn't fix it I'm gonna go insane).... Because Lancer and I aren't the only people having this problem and Fulton can be a stone wall some times.  

Edited March 20, 2014 by dingdong

[Lancer1]

Dingdong, that' funny (it sucks) that they replied to you, and not me. I sent them numerous emails about them sending me the wrong part, they never did reply.  I would check with DSG arms, they are an ArmaLite distributor, and they were right on the money with this gas tube (and their technician new the difference in gas tube lengths).  It fixed my problem.  See if DSG has it in stock, don't even mess with Delta3 if you don't have to.  It took me a few months to get all the kinks out of that build, now it works flawlessly, and I would trust that gun in combat.  I had to do extensive research, I changed the extractor spring, and also put an adjustable gas block on there.  Finally, I got it to work as the design is intended.  Please let me know if I can be of any help with your issues.  Actually, I finally got one from ArmaLite (actual), it was on backorder from them, but they finally sent it to me.  Now I have two of them, plus the other one that is too short.  Anyway, let me know if I can provide anything else to help.

[Rsquared]

I've dealt with Delta 3 also (on and off). They can be a good source for parts........but they can also be a black hole sometimes. I primarily get my Armalite parts from Armalite...or 762 SASS. Now don't get me wrong. I've gotten parts out of Delta 3 before. In a timely manner have you. But other times...nothing. Not even an email. Phone doesn't pick-up. I realize that last year was a pretty brutal year for part's supplier's. But those times are fading away as things get (kinda) back to normal.

[dingdong]

(As of this posting) I checked with 762SASS and they are out of the full length gas tubes.  As for Armalite, they charge $16 to ship a $12 tube.  DSG seems reasonable ($6 for 2-day USPS or $24 for 3 day UPS?... WTF?)..... Like I said, I'll post later when I get the part and try it on the range. 

Edited March 21, 2014 by dingdong

[dingdong]

I went to Criterion's website (the folks that make Fulton's barrels) and they seem to think that "AR10 match grade barrels are designed for DPMS/Remington/FA pattern rifles."...... their words, not mine (http://criterionbarrels.com/products/ar-10-barrels).  It could explain the mix-up, but I'm at loss as to how a barrel manufacturer and parts/rifle company can both overlook something like that..... Maybe I'm just hung up on nomenclature, or maybe its just a marketing/website gaff...... Or maybe (likely) they really don't know the difference and are putting AR10 barrels in to LR308 based rifles.

 

P.S. I ordered my AR10 gas tube from Delta3 and it should be here soon.  I'll post the results (good or bad) by next week.

[Lancer1]

Well what do you know?  The barrel that I put on my "DPMS" platform upper receiver, was indeed from Fulton Armory.  And it would not work with a regular rifle length gas tube, I had to hunt down an ArmaLite rifle length gas tube to get it to work right.  The barrel shoots deadly accurately, it is stainless steel, 22".   I'm happy with the barrel, it just took me some research and time to figure all that out.  This all makes sense.  I wonder where the difference lies, is it in the barrel extension?  Or is the length from the breech to the gas block (where the gas port is) longer than a barrel made for a DPMS rifle?  Your conversation with the folks a Criterion would have been of special interest to me while I was wondering why I had stove pipes, failure to feeds.  I really started to figure it out from someone on this site, he said something like "how far into the upper receiver should the gas tube reach".  Then I started to look at my other DPMS (the one that works), and I noticed that the gas tube I had on the FA barrel only went it about half as far as the other one (other DPMS upper).  Anyway, look at the pictures I posted and you can see the difference in how far the tube reaches into the upper receiver.  Don't forget to make sure your extractor spring is stout enough (five coil, also from FA), and also to put that little black "O" ring over the extractor spring.  That was part of my problem.  The extractor was letting go of the empty case too soon, and the bolt went all the way back, picked up another round, and tried to cram it into the chamber along with the dropped empty (stove pipe).  These things are a bit finicky, don't let it beat you down, keep trying because when everything works like it should, it is a beautiful thing.  I have an MIA, M1 Garand, 3 AR-15's, and two LR-308's (clone).  I think the DPMS type 308 with the FA barrel on it is my favorite shooter out of all of them.  Something else that makes it my favorite is being able to handload for it.  168 gran HPBT's, over Varget, or W 748, or a number of other powders, really brings out the "MOA" on it.

[survivalshop]

  There's a lot of people on this forum that have FA barrels on there DPMS type rifles with rifle length gas system & have no problem with std AR 15 rifle length gas tubes , I have two of them myself . One a 20" & the other a 16" .

  There's more to this than saying all FA barrels need a AR 10 longer gas tube . Wonder if there are some mis matched or miss designated barrels made for FA.  ?

 

 My barrels were made for a DPMS rife , what did , if any thing did they change ?

[98Z5V]

^^^  Yep.  My Fulton Armory 18.5" SS barrel uses a rifle gas system, and I'm NOT running an Armalite-length rifle gas tube. 

[Lancer1]

I did not intend to say that "all" FA barrels on DPMS type rifles need an AR 10 gas tube.  If I said that, then I need to be more articulate when posting.  All I'm saying is "MY" FA barrel required the use of the longer, AR 10 gas tube for it to function correctly.  With the standard AR 15 rifle length tube, I realized that the bolt would not hold open on an empty magazine.  So, after I put the ArmaLite gas tube in, the bolt carrier held back by the bolt catch, as it is supposed to do.  In my case, would you not agree that this is an indicator?  This circumstance led me to understand that the bolt carrier was not being sent back far enough to engage the bolt catch / hang on the empty magazine (with standard gas tube installed).  I'm happy for everyone that has a DPMS type rifle, with a FA barrel, and use a standard AR 15 rifle length gas tube. I notice that FA no longer offers the 22" barrel for sale.  I notice that I was not the only person to have trouble with insufficient (under gassing) pressure to throw the bolt carrier back far enough (and I have the correct buffer, and spring).  Also, I could plainly see that the two gas tubes did not extend into the upper receiver equally.  Step by step, I was able to find out why my rifle did not function correctly, and now it does. I've seen many times on this site (good advise) to check and see if the bolt carrier is held back on an empty magazine, because that is an indicator. 

[survivalshop]

   That's why I wondered if they made some barrels wrong or out of spec. . We are all for getting a rifle to work properly , no matter what needs to be done or what part or parts may need to be changed out . We don't always get the complete picture from some of the manufacturers . Your case is just one of those where you have to figure it out with out there help .  <thumbsup>

Edited March 25, 2014 by survivalshop

[Robocop1051]

WTG on figuring out what was wrong! That had to be unnerving. I hate spending a shiit ton of $$$ to find out something doesn't work. Especially when it could be one tiny part. Glad you were able to fix it on the cheaper side.

[dingdong]

Well, It worked.   I didn't clean my rifle since the last range session and it's functioning at least 200% better with the correct (or incorrect depending on how you look at it) gas tube, a dry bolt, and month old carbon residue.  My gun ran through a box of 168gr Federal match and a box of 155gr TAP without short stroking once.  It did not, however, cycle once with 165gr Federal bonded (at least dirty it didn't). The bonded stuff was short stroking the gun on every shot just like before.... But at least it liked 2 out of the 3 of my available ammo types.

 

Thank you again Lancer for starting this thread and everyone else for adding.

 

$12 gas tube (1/3 of 1% of the total cost of the gun).

[Lancer1]

dingdong, look at you, you got it to work <thumbsup>.  Clean that thing up and run the bolt/carrier nice and lubed up (I even used Mobile ONE)( I read that I should use grease on exposed sliding parts, and oil in confined areas, so it doesn't sling out).  What about the extractor, could it be letting go of the empty brass too soon after it gets jerked out of the chamber? (if so, the empty case just lays there/bounces around in the chamber/magazine area, and interferes with the incoming round)  With the Federal Bonded ammo, did you check to see if the bolt will hang open on an empty magazine? (just load one round in the mag, then shoot, see if the bolt carrier hangs back)  Even though I had paid like $265 for a JP Enhanced bolt, I had to replace the extractor spring, and add the little rubber o ring (around the spring) to stiffen it up. (Extractor spring, 4 coil (no good), 5 coil spring (Fulton Armory), worked good!).  I kept chipping away at all these quirks, now it shoots any ammunition I put in it.  I also put an adjustable gas block on there, but I left it wide open (full charge).  It really slams the bolt back hard (although there is not much felt recoil), I almost thought it was "over gassed", but no, it cycles like it should.  Please don't stop checking on all these issues, I had to go to the range like 5 times before I got ALL the kinks out.  It should really cycle with any appropriate ammunition. 165gr Federal Bonded included. It should also loosen up as you shoot 200, 300 rounds.  What say you Double D?

[dingdong]

It extracted/ejected just fine even when it was short stroking.  However, before I put in the AR10 gas tube the bolt cycled back far enough to eject but not far enough to pick up a new round or hold-open on an empty mag.  With the short gas tube you could feel the sluggishness in the bolt.  Now it feels like an auto loading .308 should feel and cycles like an auto loading .308 should cycle.  The 165gr stuff not cycling doesn't bother me.  I just tested it because I had it, and to be honest it could be because the ammo is simply old stock.  The most abundant ammo I have is 155gr TAP and it cycles just fine, and if it aint broke (for my purposes) I'm not going to "fix" it.

[Lancer1]

Outstanding. I'm glad you got it to work. And, if you are happy with it, that's all that matters !

[cantshootafish]

Wow!  Thanks to all of you for this info. I am in the process of building a DPMS base .308 from a 80% lower and have everything except the gas block, barrel, forend and gas tube.  Two buddies of mine are doing the same thing and we are ordering parts together to save on shipping from when we started this project 8 months ago.  We have done a few .223 rifles before this for ourselves so are familiar with it all.

 

Any further info would be greatly appreciated.  The biggest problem now seems to be that everyone is out of stock on any good deals on barrels.  I did not know that the SASS parts were only compatible with their other parts.  You just saved me a big headache later.  Thanks much.