Great build. Bison suppose to have great barrels. Guess their specs is the SPCII chamber, 1/11 twist 4 groove?
I have a YHM 16" barrel upper SPCII but the faster 1/10" twist but wanted one for hunting with a slower twist. Just picked up a second hand upper with the 18" Bison SPCII 1/11" 4 twist (have not shot it yet) to see how much velocity gain I can get over the YHM barrel with my reloads.