Just got back from the range. I finally got all the parts for my new AR build that included a new (and one of the last) 18" barrels from Tim at Cardinal Armory. This range trip let me try out the YHM upper receiver, Noveske gas tube, and Micro Best 6.8 bolt. Everything worked well without a hitch. I was easily shooting sub-moa right from the beginning. My wife has my camera on a trip so I don't have any pics, but you guys all know what bullet holes in paper look like :)
For the record, the rifle is built with a YHM rifle length forearm, YHM low-profile gas block, YHM scope riser, A2 butstock from Model 1, RRA (I think) lower parts kit from RB Precision, and a super-cheap Simmons 3-9x40 that I pulled off of my Savage rifle package.
I was also shooting Sierra 110gn pro hunters over 28gn of H322. I found that to be a very good load in my old 6-groove barrel as well.
So I am stoked! Everything is working out well. Now I just have to sit and wait for the barrels.