I bought a used upper a couple years ago...A2 with government profile 1:7 chromelined, yada, yada (like the ones CMMG was selling two years ago), and it ran ok until it got hot. At first I thought it was the ammo (Q3131A), so I changed to Winchester White Box 62gr. I still had FTExtract. I tried Black Hills, American Eagle and UMC, but when it got hot, a case would get stuck.
I replaced the extractor spring and insert, added a D-fender, cleaned the chamber thoroughly, and even had headspace checked. I didn't change the extractor since I could not find any problems with it.
I finally contacted DPMS in December to see about what else I could do. I didn't expect anything free or warranty work since I wasn't the original owner, and had fired Q3131A in it before I found out differently. Shane got back with me immediately, and told me to send the upper in. I did. They got it just after Christmas, and he said that it may be a couple weeks before they could get on it. Last Monday, I get a box in the mail with my upper (weeks earlier than I expected). Included was a tech report which said "replaced extractor" and "fired 20 rounds."
I was happy to have my upper back, but was a little skeptical that it was fixed by only test firing 20 rounds. Most of the time it doesn't have problems until 50-70 rounds, fired in rapid succession. I figured I would take the upper to the range and 120 rounds of WWB 62gr FMJ, since the WWB seems to be dirtier and had a higher failure rate in my upper. I put a little CLP on the bolt carrier rails and left the rest of the gun dry.
120 rounds later, fired in rapid succession (almost as fast as I could load and pull the trigger), resulted in a smile to my face because of no failures of any kind. I feel a little dumb for not replacing the extractor myself, but with all the internet gossip on tight chambers and such, I was convinced it was the chamber. My test proved otherwise.
Anyway, I just wanted to say that DPMS did right by me. Excellent communication, speedy service, and was not charged for shipping or work involved. Thanks to Shane and others at DPMS. You guys are good to go!