Fishco Posted November 9, 2011 Report Share Posted November 9, 2011 I have built 4 DPMS lr-308 rifle and my last one has me baffled! The problem is that it won't cycle a round and load another, hold on, its not a magazine problem. You can manually cycle rounds and emptys through the magazine and no problem.When I fire it, the bolt comes back about 1/2-3/4 inch and thats it, you can go ahead and manually cycle it out, but the gun wont do it.I have tried this with a 16" & 20" barrel and the same issue.I have tried other barrells on this lower and no problem.I have swap complete carriers and still same issue.The only thing I have found is that the gas tube doesn't come into the upper as far as my others.It is about 1/4-5/16 inch short, therefore it is not seating in the gas carrier as far as my others.I have re-torqued the barrel many times and it still wont go any deeper, changed the gas blocks and still the same.All parts are factory DPMS, they won't help me since they didn't assemble it...What the crap have I done???Please help! Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 9, 2011 Report Share Posted November 9, 2011 Weird gas tube, man. That's about all I can think of - can it and pick up another one. What's in the pics could definitely be what's causing your problem. Worth a try, since the gas tubes are less than $15. I'd start there first. Quote Link to comment Share on other sites More sharing options...
Fishco Posted November 10, 2011 Author Report Share Posted November 10, 2011 I have new gas tubes ordered, but the one installed is the correct lenght...... Quote Link to comment Share on other sites More sharing options...
Fishco Posted November 10, 2011 Author Report Share Posted November 10, 2011 I am starting to think the reciever is defective, maybe where the nut jams against the barrell, possible too long of reciever? Quote Link to comment Share on other sites More sharing options...
IM_JOHNNYV Posted November 10, 2011 Report Share Posted November 10, 2011 Could the gas hole be drill too far forward? Quote Link to comment Share on other sites More sharing options...
Fishco Posted November 10, 2011 Author Report Share Posted November 10, 2011 Everything seems to be in the right spot. Hole looks to be correct, its the same problem on the 16" & 20" barrells on this particular upper. Quote Link to comment Share on other sites More sharing options...
imschur Posted November 10, 2011 Report Share Posted November 10, 2011 is the gas block drilled properly? Quote Link to comment Share on other sites More sharing options...
Fishco Posted November 10, 2011 Author Report Share Posted November 10, 2011 Yes, everything thing is drilled correctly...I just notiiced that when I compare it to other guns I have it seems that maybe the barrell nut is too long? Is this possible??? Quote Link to comment Share on other sites More sharing options...
Fishco Posted November 10, 2011 Author Report Share Posted November 10, 2011 Correction barrel extension..... Quote Link to comment Share on other sites More sharing options...
Fishco Posted November 10, 2011 Author Report Share Posted November 10, 2011 Heck, theres only to possibilities, the barrel extension is too long or the front sight/gas block is located to far forward.Funny its the same on 2 barrels....I don't know, you would think I could send this to DPMS, but they said since they din't assemble the gun, NO CAN DO>>> Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 10, 2011 Report Share Posted November 10, 2011 Same thing on a 20" and a 16". Chances are slim, man, just sayin'. Barrel extension being too long on two completely different barrels, or improperly drilled, and probably not from the same batch, either - not very likely, seriously. Could happen, but I'd look at something else first.Problem with the upper, maybe? <dontknow> Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 10, 2011 Report Share Posted November 10, 2011 Someone sell you some RRA upper parts when you weren't looking?... <dontknow> Quote Link to comment Share on other sites More sharing options...
Fishco Posted November 10, 2011 Author Report Share Posted November 10, 2011 Upper came straight from DPMS......Man I am at a loss. goint to completely break down one of my others and compare upper to upper... Quote Link to comment Share on other sites More sharing options...
Robocop1051 Posted November 10, 2011 Report Share Posted November 10, 2011 I'm jumping on the gas tube bandwagon. If you're absolutely positive the length is correct, and that the gas block is seated properly... What about the roll pin location? Could the roll pin hole on the tube be out of spec so that the tube is seated too deep in the gas block? Could the roll pin hole on the gas block be out of spec?I can't imagine an upper being 1/4" out of spec. That's a lot of distance for machined parts. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 10, 2011 Report Share Posted November 10, 2011 Gas block on backwards? I just re-read everything, and it's not even ejecting casings. BCG is moving 1/2 to 3/4" when you fire - recoil from firing could do that, possibly. Sounds like there's no gas going through it, which is why I ask about the gas block.More pics would help, too. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted November 10, 2011 Report Share Posted November 10, 2011 You would have to compare the non working gas system to a working system ,meaning all the components .If the gas tube is too short , not far enough in the carrier key , it would cause a timing problem & under gassed.Were the 20" & 16" both same length gas systems ?Were you using the same gas block/tube on on both barrels ?I would look as has been said , gas tube length, gas block configuration( out of spec., holes in the wrong place or too deep into block ) , & definitely check the upper 's spec's compared to another.If you need measurements ,we can help.UHH, gas block on back wards ? I think they only have one entrance for the gas tube. <dontknow> Quote Link to comment Share on other sites More sharing options...
Fishco Posted November 10, 2011 Author Report Share Posted November 10, 2011 This is what I know so far:1: Tried several gas blocks, roll pin location is correct, not on backwards, can blow through gas tube and air passes through.2: Checked and re-checked several gas tubes and are passing air test and all are correct lenght3: All parts are direct from DPMS4: Tried 2 diffrent DPMS Barrels, a 16" and a 20" and still have same problem.So it has to be 1 of 3 things:1: Both barrels have in-correct located gas block mounting area2: Both barrels have in-correct barrel extensionsI highly doubt that 1 or 2 is the caseor3: Upper is machined in-correctlyI am leaning on the upper being defective.I will disassemble on of my workin guns tonight and compare.I will add more photos.Thanks for all the input, please keep it coming, I need help to solve the puzzle! Quote Link to comment Share on other sites More sharing options...
Jgun Posted November 10, 2011 Report Share Posted November 10, 2011 Fishco, Based on the parts you've swapped out, and the fact that the problem remains, I'd be guessing that it must be somewhere in the parts that your not changing. You said that you tried different barrels, right, so it's not your barrel extension. I'm assuming that you've swapped gas blocks and tubes along with those barrels, if not, they can't be ruled out as the cause. I haven't used a DPMS gas block, but a PRI low pro could theoreticaly be installed backward, but that would locate your gas tube too deep into the upper not too shallow as you describe so I doubt thats the problem, The barrel nut should have no effect on the gas tube location. when the carrier comes forward the bolt seats against the barrel extension, so the dimensional relation of the back of the barrel extension to the back of the gas tube is something I would check. You say you have other DPMS .308 ARs. Can you check that measurement and compare it to guns that you know work? If the measurement is the same your problem is not caused by the gas tube being mislocated. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 11, 2011 Report Share Posted November 11, 2011 UHH, gas block on back wards ? I think they only have one entrance for the gas tube. <dontknow>Yep, it could happen. PRI for example, the gas tube hole is drilled straight through, all the way. You could get the tube in it from either side, and roll-pin it in place, but it's not going to work if it's not correct. I'll grab a pic of my PRI.I don't know how many others are drilled all the way through. <thumbsup>Looking at the front of my gas tube, out of the end of the PRI lo-pro block. You could put this on backwards, and pin it. How many others out there are drilled all the way through?... Quote Link to comment Share on other sites More sharing options...
Jgun Posted November 11, 2011 Report Share Posted November 11, 2011 Of course with the PRI, if you were to mistakenly put it on backwards, and you mounted the gas block against the shoulder on the barrel, the gas port in the barrel wouldn't line up with the hole in the gas block anyway, so you'd have a single shot rifle that wouldn't cycle at all. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 11, 2011 Report Share Posted November 11, 2011 Exactly. <thumbsup> Quote Link to comment Share on other sites More sharing options...
Fishco Posted November 11, 2011 Author Report Share Posted November 11, 2011 I will be posting back my findings once I take apart the non working gun and one that works...Hang in there, we are going to solve this mystery! Quote Link to comment Share on other sites More sharing options...
survivalshop Posted November 12, 2011 Report Share Posted November 12, 2011 Yep, it could happen. PRI for example, the gas tube hole is drilled straight through, all the way. You could get the tube in it from either side, and roll-pin it in place, but it's not going to work if it's not correct. I'll grab a pic of my PRI.I don't know how many others are drilled all the way through. <thumbsup>Looking at the front of my gas tube, out of the end of the PRI lo-pro block. You could put this on backwards, and pin it. How many others out there are drilled all the way through?...Well , I've not seen that one before . How many more out there with a hole all the way through ? I have at least five different manufacturers gas blocks in there & a std front sight & none of them have a hole through them .I guess once the gas tube sealed, it wouldn't matter .Different barrels , gas blocks & tubes , I can't see the sight shoulder on both barrels being out of spec. or both gas blocks .I 'm going to assume you have a rifle length gas system or are you saying even with two different gas systems ( different length barrels ), the gas tube is in the same position in the upper receiver.A partialy pluged gas hole will do the FTE , you are sure the gas holes are lined up .The rifle length gas tube in my hand is 15 1/8 " long with in +- . Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 12, 2011 Report Share Posted November 12, 2011 I have no idea, brother, but I have two PRI blocks, and both are like that. I thought I had another that was drilled all the way through, but I need to go through the guns to find it. I'll keep looking. I know there's one of them that the gas tube is flush with the very end of the block, so it's silver gas tube and black block, all flush at the front. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted November 15, 2011 Report Share Posted November 15, 2011 Any update ? Quote Link to comment Share on other sites More sharing options...
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