Lancer1

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.

Robocop, thanks for your reply. Yes, I do see a difference in the distance, i.e, the shoulder were the gas block meets the larger diameter of the barrel on the Fulton Armory barrel is set farther foward by about 3/8" than the shoulder on the blue barrel (see picture). Both gas blocks are bumped up against the shoulder (larger barrel diameter) and are clamped tight. I just happen to notice the one gas tube did not enter the upper receiver as far on one, as it did the other.

Hello all, great forum, I've spent many hours gleaning important information from the good folks on this site. I have two LR-308 type builds. The issue I have is failure to feed with one of them. I've read many of the posts concerning this issue, and wanted to run my thesis past your collective knowledge. The offending culprit is put together with a Fulton Armory 20" stailess barrel, and a real DPMS upper receiver. I'm not sure the BCG is traveling back far enough to eject, and then pick up the next round. One issue is the poor performance of the DPMS 10 round mags. The lips do not allow the rounds to peek up quite far enough, so I fixed that issue with an after market mag, higher lips, better feeding. My issue now is a bit of a quandary; Although I purchase all DPMS compatible parts, I suspect that the FA barrel requires an AR-10 specific gas tube. Look at the picture, both upper receivers have the same dimensions, but the gas tube does not protrude into the upper quite as far. Both gas tubes are standard rifle lenght gas tubes (15-1/8") long. I'm thinking the gas tube in the FA barrelled upper does not engage the Carrier Key quite enough, thus not delivering a proper pressure to blow the BCG all the way back. The Armalite web site says their gas tube is 15-1/2" OAL, and I know a standard AR rifle length gas tube is 15-1/8". In my picture, that looks just about the differnce in the protruding gas tubes. What do you guys think? Might I be on the right track? Any inputs are welcome. Thanks. These rifles are deadly accurate, with both factory, and my handloaded ammo, albeit I have to shoot the one that won't feed as a "single shot" ::). The upper on the bottom is the one in question.