Got my Banshee upper tuned very well with my Spike's lower and a Magpul CTR stock using a Kynshot RB 5005 hydraulic buffer and a standard carbine round wire spring. Blazer Brass FMJ using an Endomag insert in a Pmag gen 3. 3k rounds downrange so far without FTF/ FTE. ~666 RoF.
CMMG Banshee upper on Spike's Cal-Multi Lower, Endomag Pmag insert, KAW Fat LC