Are you swabbing the barrel between shots? That will often times make the shots more consistent. You are probably on the right track with trying different powerbelt weights and different charges. I personally shoot a CVA Staghorn and it will shoot the 348 grain pure lead hollow points or the 245 grain Aero Tips real will with 90-100 grains of loose powder. 90 grains if I shoot Goex and 100 grains if I shoot Clean Shot. If powerbelts are what you want to shoot then you have to try different combinations. I had the same experience with the 295 grains as you did. I really thought I was on to something when I first started shooting them but back at the 100 yard station they shot about a 6 inch group. The others do much better with the open sights.

In my Staghorn, I get good results shooting 375 grain Buffalo Bullet SSB sabots. I shoot them with 100 grains of Goex 2f. I also have good luck with the 240 grain T/C Cheap Shots and T/C Mag Express XTP's and 100 grains of loose powder. All of them are real game stoppers. Something else you might experiment with if you get a chance...

Good luck with your rifle.