Way to much powder for Power Belts, they work best with 70 or 80 gr and they are much more accurate with less powder as well as the known fact the the will fragment on the surface with that kind of velocity.
If you are set on shooting that type of bullet try a Saber Tooth 300gr with 100 gr powder.
For a Remington Genesis I would try the new Hornady FPB several people have had excellent results with them.
For a flat shooting high velocity load I would recommend a 250 gr Shock Wave 90, 100 and 110 gr of powder.
For a really good deer load up to 150 yds a 250 Gold Dot with 90, 100 and 110 gr of powder.
With a muzzle loader you need to try several different loads of powder and loose is not only much more economical it is also much better for finding an accurate load, if you feel you need to stay with pellets then try a 110 gr load. Lee