The only upper I ever had that problem with repeatedly
...not counting the occasional one due to having to use worn out 30 year old pre-ban mags. was a 10" carbine barrel with a mock moderator on it.
The extractor seemed just fine and worked just fine in anything else I tried it in, so I swore it was a pressure/dwell issue. Played around with fat gas tubes etc to changes things with no luck. I put an upgrade kit in the bolt (spring, o-ring, rubber do-hickiee) and the problem went away. 
Complete thread:
- AR double feed continues... - 
rob, 
2015-07-03, 19:32 
- AR double feed continues... - bj, 2015-07-03, 19:55
 - Another mag and factory ammo. Eliminate's everything - 
Rob Leahy, 
2015-07-03, 21:37
- ^^^^This is the Ticket^^^^^^^^ - 
Miles, 
2015-07-03, 22:00
- suspecting brass right now... - 
rob, 
2015-07-03, 23:02
- suspecting brass right now - mcassill, 2015-07-04, 02:26
 
 
 - suspecting brass right now... - 
rob, 
2015-07-03, 23:02
 
 - ^^^^This is the Ticket^^^^^^^^ - 
Miles, 
2015-07-03, 22:00
 - AR double feed continues... - 
Bob Hatfield, 
2015-07-04, 05:32
- Actually it's a FTE/FTF... - 
rob, 
2015-07-04, 08:34
- What buffer do you have in the riffle? - 
Miles, 
2015-07-04, 23:09
- AR Stoner Mil-spec buffer tube and whatever... - 
rob, 
2015-07-04, 23:27
- So far the plan is to get to the range with... - 
rob, 
2015-07-04, 23:35
- it's very difficult - 
Miles, 
2015-07-05, 13:28
- Great info... - rob, 2015-07-05, 13:38
 
 
 - it's very difficult - 
Miles, 
2015-07-05, 13:28
 
 - So far the plan is to get to the range with... - 
rob, 
2015-07-04, 23:35
 
 - AR Stoner Mil-spec buffer tube and whatever... - 
rob, 
2015-07-04, 23:27
 
 - What buffer do you have in the riffle? - 
Miles, 
2015-07-04, 23:09
 - Makes me see and appreciate the beauty and simplicity of.... - rob, 2015-07-04, 08:39
 
 - Actually it's a FTE/FTF... - 
rob, 
2015-07-04, 08:34
 - AR double feed continues... - 
jgt, 
2015-07-04, 07:44
- That is true except on an AR.... - 
rob, 
2015-07-04, 08:36
- The only upper I ever had that problem with repeatedly - 
cas, 
2015-07-04, 10:17
- i ordered the BCM extractor upgrade parts this morning so... - rob, 2015-07-04, 10:54
 
 
 - The only upper I ever had that problem with repeatedly - 
cas, 
2015-07-04, 10:17
 
 - That is true except on an AR.... - 
rob, 
2015-07-04, 08:36