I got a complete Bushmaster 14.5" A2 M4 style upper for my preban Eaqle Arms lower. The lower sports a Colt 4-position telestock with "H" buffer. I put about 300 rounds through it without a single hitch...it was flawless. Then I sent the upper back to have the receiver replaced (poor machining) and to have the sights straightened out (I know, I know....shoulda left well enough alone). Then I get it back and all the sudden it starts failing to extract the cases from the chamber. The bolt comes right off the rim of the case and then tries to chamber another round behind it. The case is not sticking as far as I can tell. When I have a jam, I lock the bolt back and tap the butt of the stock on the bench, and the spent case falls right out. The entire gun was spotless when I started to have problems, so I know it's not a dirty chamber.
I am using the same mags I've always used...USGI 20's and 30's. Sometimes (RARELY) I can go through a whole mag without a FTE...sometimes it happens about every 5th round...sometimes it's every other round. I've tried PMC, Lake City M193, and Winchester Q3131 and get the same results with all 3. I thought the extractor spring might be too weak, or maybe the extractor was damaged. So I put in a brand new bolt assembly, but it made no difference...if anything it was worse because the new bolt had a McFarland gas ring. It seems like the bolt/carrier is getting too much gas pressure or something...and the extractor is just blowing right past the rim of the case before chamber pressures have a chance to settle. I just thought it was strange that the first 300 rounds were flawless, and now all the sudden it's giving me nothing but trouble.
I thought about trying one of those D-Fender extractor rings that Fulton Armory sells...it's supposed to increase extractor tension. But I cringe at the thought of paying $13 for a little plastic doohickey to fix a problem that shouldn't exist in the first place...and then find out it didn't even cure my problem 100%. Any ideas on what else I could try? I hate to send my upper back to Bushmaster again, but that might be my only choice...I just wish they had test fired my upper before they returned it.