Couple of things to consider. Your rifle is an in line right? With a tighter twist, say 26 or 28? Power belts are a full up bullet (no sabot just a plastic end on it). Try a sabotted round in it. I use a 360 grain Keith nose sabot for my 54 cal Thunderhawk (Google Precision Rifle). I use it for both Elk and Deer with a peep site (no scopes allowed on ML in Washington state). It is as accurate a load as I have every shot and has never failed me. The twist on my rifle is 38 and Powerbelts do not work well in it. Another quirky thing I learned. If your rifle has a floating barrel, be sure to rest the stock grip on the sand bag not the barrel alone. That one drove me crazy until a really experienced black powder guy helped me out with it. I use 110 grains of 777.

Steve