Your switching to a different brand of projectile was your first mistake. When you're sighted in with Powerbelts, unfortunatly your stuck shooting them. I have a CVA Staghorn Magnum and it shoots Powerbelts in 245 grain with 90 gr of Goex 2f excellent. You switch to something else and you have to make sure to test the load.

Try some 240 grain XTP's with 80 grains of powder. Shoot them first somewhere before you hunt. They should shoot well out of your rifle. At least my friends Beartooth shoots them well and they are basically the same thing. Of course that's no guarantee that your rifle will shoot them.