Okay, need some help here. I've been playing with a 6.8 barrel that I've been having a number of FTFs. Happens either when initally loading the weapon and when firing. It is NOT consistently from the left or right side of the magazine. One FTF has the round hanging up on the M4 ramps. The other, the bolt will not fully seat and the round is not captured by the extractor, but in front of it.
You can see in the pic where the barrel is shaving brass off of the cases. You can also see, even though the pic is horrible, where the tips of the M4 ramps are picking up brass as well.
Barrel is 12.5" stainless. Supposedly a Rock Barrel. Picked it up from Capn Crunch in some trades awhile back. Was chambered and such by ABS. I'm running an H buffer.