Not really a review, just my impressions.
Shot the BM upper today at my local indoor 25 yard range.
Put 30 rounds of Remington 115 FMJ and 10 rounds of SSA 90 Gr TNT through it. At $1.00 a round, I couldn't go real crazy.
I did not have any malfunction.
The only issue I had was seating the first round in the chamber. If I used the bolt release, no problem. If I tried to sling shot it, the round wouldn't feed correctly. It would hang-up half way in the chamber and lock the bolt open. I would than have the pull the bolt back a little and re-release.
I didn't find this a big issue, and in all honesty, it could have been my fault. I added the O-ring bushing to the extractor spring like I do on all my .223/5.56's. Not sure if this is needed on the 6.8.
I shot a slow fire group while leaning against the side of the shooting booth at 25 yards. I was able to keep all rounds within a fist size group. Obviously not a true test of accuracy, but for my intended purposes (CQB ranges), I was happy.
I didn't use the irons at all to see if the shorter non-F marked front sight post would be a problem.
What was nice is I pulled optic I was using (Trijicon Tri-power) off a .223/5.56 upper I had and stuck it on the 6.8. It didn't require any re-zeroing with the 115 gr. bullet for the type of shooting I did. (Maybe If I was doing more precise shooting it may have needed a turn here or there). The 90 gr. bullets seemed to shoot a little low.
I also dumped a fairly quick 10 rounds without any problems (not too quick though, indoor range rules on no rapid fire).
I stripped the BCG out at home and didn't see any abnormal wear. Really wasn't even that dirty (although it was only 40 rounds of quaility ammo).
So overall, I'm happy with my $500 BM upper.