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Posted: 6/29/2013 7:10:14 PM EDT
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Bought a stripped SI Defense lower, lpk and assmbled the lower. I bought an unfired complete 18" DPMS 308 uppe(18" stainless 1/10 twist barrel, bolt carrier group, charging handle & 12" Troy battle )
http://www.gunbroker.com/Auction/ViewItem.aspx?Item=341077113 I brought the gun out and fired the first round, but it never cycled the next round. I manually ejected the round, cleaned the barrel, put the mag back in and fired again. Again the gun didnt cycle and i had to manually eject the round and feed another in. By manually eject, i mean i had to use pull the charging handle back. I read about making sure everything was lubed up well and made sure i coated the BCG with a layer of oil and sprayed the upper with Remoil. My buddy had his DPMS 308 with us, so i swapped lowers and it didn't make a difference. My lower had an A2 fixed stock, my buddies was paired with a Magpul PRS. I swapped BCGs and still ran into the same problem with my build. I believe that narrows it down to a gas port/tube/alignment issue. My question for you guys is what should my next step be? Thanks, Dave |
| Verify if the gas block was installed properly. Remove the bolt, plug the chamber, then blow down the barrel from the muzzle end to see if air seems to be getting through the gas port OK (sometimes a little tricky depending on what kind of muzzle device you have but you get the idea - need to verify the gas block/gas port/gas tube are all open and working properly). |
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Do you have the correct buffer and spring? AR15 buffers/springs won't work in a .308. I do, the buffer and spring work on my other .308 build. (RedXArms Upper/TM Lower) Thanks for the suggestions so far, i'm working with the seller to resolve the issue, but still open to suggestions. Dave |
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Dumb question I know - are you sure your bolt has the gas rings installed and they are not lined up?  I put the bcg from this gun in my other 308 and the other 308 cycles fine. I ruled out every part but the upper by trying them in my other DPMS style 308. Dave |
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Thanks for all the help and suggestions! I youtube'd how to disassemble the upper and found that, in fact, the gas rod was flipped up side down. I lined the gas tube hole up with the gas block, pinned it back up, reassembled and put a bunch of rounds through it trouble free!!!
Thanks again! Dave |
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How was the gas tube installed upside down and assembled? Wouldn't it have to be bent up to go through the hole in the receiver? I would think it would prevent the bolt carrier from closing also. Im guessing it was a straight tube maybe? I agree. It would cause the proiblem, but would have caused others as well. And I have never seen a straight gas tube. You would need a gas block with a higher tube opening. |
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There are some straight gas tubes out there, I know Wilson makes one, and yes they use a gas block with a higher tube opening. Don't know if that's what the OP has though. Been there done ths once with a straight tube on my 2nd build. It was quite frustrating. |
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Im confused at how someone could install a gas tube upside down. Especially one with a bend in it. Yeah me two It can be done... trust me, I've had to fix two uppers over the years that were done wrong. How? Because someone was NOT paying attention... When I read the OP's post, it was almost obvious to me what the problem was. |
| After you check that the tube is not on upside down (we see it happen all the time on this web site) check that the gas block is not on backwards if it is a low pro and open on both ends. Then, MEASURE the difference between the barrel shoulder to the centerline of the gas port then do the same from the rear face of the gas block to the centerline if its port. Subtract and space the gas block off the barrel shoulder by this amount. Too many people just slam the gas block up against the barrel shoulder and call it good, then wonder why their rifle will not function when they have blocked the gas port. That happens all the time with new builders. |
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