Ditch the PowerBelts and the 777...Stick with loose powder in either Pyrodex RS or better yet, Goex FFF...

Go to either a .44 or .45 caliber pistol bullet inside the appropriate sabot...

I like the .429 300gr Hornady XTPs inside a Harvester plain green sabot but they are hard to find right now...Many use the .429, 300gr or you can go to the 250 or 300gr .451 Hornadys...Then go to a black sabot, I use the MMP-24 in this situation...

Powder charge is usually 80-90grs depending upon the rifle...

And, I always clean between shots and sight in with a clean barrel as that's what I hunt with...