I've built dozens of uppers using ballistic advantage barrels all 223 wylde or 5.55, well one .308. All have been pretty good, every (about 6)18 SPR stainless barrel upper I've built has shot lights out. I've had some 16s that were just ok, one 223 wylde 16 that could group for sheer. The 10-14.5 i really didn't try to test accuracy much since they were just short blaster builds.
The last 5 or so I paired with BKF mod 0 thermal fit uppers, freezing the barrel overnight and heating the upper is definitely required, very tight fit.
The last 5 or so I paired with BKF mod 0 thermal fit uppers, freezing the barrel overnight and heating the upper is definitely required, very tight fit.