Any of the Knight videos you watch they tell you to use FFg grade powder in the Knight rifles. I personally shoot Goex 3f in my Wolverine II and my new Knight Disc. I guess it is a matter of personal preference. I have also shot Triple Se7en but only in FFg grade because I have never found it in FFFg grade.

Good luck with your rifle. If those powderbelts and SSB's don't shoot well for you, give some 240 & 300 grain XTP's a try in the rifle. They shoot well out of my rifles. Also I shoot 250 grain Barnes Expanders and they shoot real well, but are kind of expensive to shoot....