I also have barnes expander mz's 325 gr, I have shot Scorpion Pt gold 300 gr, and 300 gr shockwaves by putting them in a 54 cal sabot for a .451-.452 bullet. They shot great and did not load hard. I have some powerbelts but do not shoot them as they actually are way to loose. They will move off the powder charge to easily plus I would have to back the powder down and my lyman prefers a 100 to 110 grains. At least in the 1:32. Now my 1:60 shoots great with 80 gr. Try the great plains conical I think you will find it deadly accurate.
I didn't ask what cal. Mine are all 54 cal. If yours is a 50 then I don't know what they prefer.