I have the same gun and it thrives on 3F Goex. With the short barrel of the WMC a faster burn is a good thing. Around 70 gr for PRB / 90 for conicals. Mine doesn't like sabots in the factory barrel (48"twist) I have a green mountain LRH barrel for it that is the same length as the white mtn. That likes 110 gr of 3F under a green crush rib sabot and 300 gr Hornady XTP in .44 cal. What projectiles are you using? Round ball?