I'm no elitist - not by a long shot, but I have been doing a ton of reading on AR-15's. I had a Colt HBAR which had and still has with it's new owner - zero issues. Once upon a time, I was looking into a DPMS AR-15 to re-satisfy my itch for an AR-15. DPMS appears to be falling into an increasingly deeper pit of manufacturers who were once building high-quality rifles, but now appear to be slipping. Manufactures like DPMS, Rock River Arms, Bushmaster, CMMG etc, were once heralded as making high quality firearms, but it's becoming increasingly apparent that quality control issues are increasing along with customer complaints. As I stated in my earlier post, DPMS is gaining notoriety as the improper cutter of chambers.
If swapping out bolt carriers did not resolve the issue, then you're left with a few other options - among them an improperly cut chamber. You may also want to check your upper for signs the carrier is hanging up on the rails, (look for burrs or flaws in the receiver). Look also at your M4 cuts, (if you have them). It is my understanding that DPMS may be improperly, or shoddily cutting their ramps and properly staking the carrier key seems to be a simple procedure which is lost on DPMS - so check your ramps and carrier key. Lastly, check your buffer and spring - it's possible that there is not enough energy at the buffer tube to properly function your rifle.
There is also one other issue with DPMS - they lie, or at the very least, twist information to make themselves look favorable - rather than actually improving/changing their manufacturing practices. Over on M4C, a member put together a now infamous "chart" of features found on most popular M4s. One could call it an elitists guide to buying Colt or Noveske, but in reality it points out the good, bad and missing in the manufacturing of AR-15's. DPMS took this information, twisted it and then posted their own "version" over on AR-15.com...
![[thinking]](/xen/styles/default/xenforo/smilies.vb/010.gif "Thinking [thinking]")
Rather than look in the mirror and improve their manufacturing standards, (or lack), DPMS appears to be on a mission of deception.
Personally, short of sending your rifle back to DPMS and
demand it be made right, I would scrap it and move on. I know it's a tough pill to swallow, but one shouldn't have to invest in a new upper or rifle - only to turn around and have it tweaked or rebuilt to specs it should have been manufactured to in the first place....
Your life may one day depend on the equipment you have and it's becoming increasingly apparent that companies like DPMS, RRA, Bushmaster etc are putting profits over people....
PS: Here's a link to "The Chart"...Rather than post a cut-n-paste of it, I've sent the entire link - it's good reading and may be an eye-opener. After you're done reading it, go to AR15.com and check the company made DPMS chart...
http://www.m4carbine.net/showthread.php?t=6642
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![[frown]](/xen/styles/default/xenforo/smilies.vb/003.gif "Frown [frown]")
Trying out some new reloads Sunday and today, which were all range brass reloads, I had a few where the extractor simply didn't engage the rim of the case. No matter how many times I tried to use the charging handle, it simply wouldn't reach the rim. I had to clear these rounds (3 out of 50 rounds) with a cleaning rod down the bore. The brass needed just a very light tap to come out, so I don't think it was a chamber issue. FWIW, the rifle hasn't been cleaned for maybe 500 rounds of mostly reloads and some Privy Partizan. But hell -- an M16 in full auto is going to probably go through alot more than that before it sees a cleaning, right? 
