tried over a hundred times to reproduce, and can't get it. However, from what I remember on range day, the failures were all on left rounds...and looked like the round "wedged" crooked in the chamber. After trying to reproduce, I thought maybe either the lip of the magazine might have a burr or be shaped down, catching the round, or maybe the mouth of the case is catching on the edge of the chamber?
Although I couldn't produce the failure manually, I set up a stop on the oprod...it kind of looks like this when the failure happens...
Attachment 121214
After watching the thing feed manually...I don't think the magazine position in the wells or any looseness are the fault

Going to the range with some friends Friday...I'll try to get a good picture when the failure reveals itself.