I would agree for the most part with the above replies. Lower your powder charge to 100 gr. and try it with the sabot you are using. If you still don’t get a good group them switch to a different sabot. I have found the T/C Shockwave 250 gr. Sabot to be very accurate out of my Knight. I am getting sub ¾” groups off the bench at 100 yards consistently.
I have never been a fan of pellets. Loose propellant has worked better for me, and I have shot both Pyrodex and Triple Seven pellets. I have found that pellets print differently and not as consistent as loose propellant out of my Knight Disc Extreme.
Good luck, and please keep us posted as to your progress.