First off, I've yet to have any malfunctions not caused by the operator/handloader. The attached 11 shot group was shot at 100 yards, PPU brass, S&B LR primers, 27.0gr RL-7, a standard weight barrel (not a BHW), Nosler "Blems" 123gr FBTIP bulk. The "low and outside" shot was me.
My point is: The "bugs" have been worked out of the x39/AR combo. It will shoot with my 300AAC uppers (3 of them), is 100 fps faster with less pressure. This group is not a "one time" event - this is "normal" for this upper/load.