Unless you just have a bunch of money to blow, why not try some of the .44/.45 sabots with cast bullets?
They don't have the OOOhh/Oooww factor, but they can handle the velocity you're shooting and will expand at that velocity, won't lead your barrel (the sabot), and your barrel twist is just right for them.
They shoot great in my sidekick & huntsman - much better than the powerbelts. I have not tried the harvester brand stuff - don't think I will.
A $20 Lee mold, a coleman stove, a cast iron pot, & some wheelweights & you have all the ML you need for life. Hard to beat that.