I shoot an evolution, and I experimented a lot with loads and bullets. I found I could shoot anywhere from 90 to 120 grains of powder pretty accurate. I use the same powerbelts you do, but I have a bunch of other bullets/sabots that I use without a problem. I did notice my accuracy fell apart when I tried 150 grains of pyrodex. Anymore, I just use 100 grains of loose powder, or two pellets for convenience when I'm hunting.
The biggest complaint I have with the rifle is the crude safetly mechanism and the rough trigger. I may try to polish some parts to smooth things out. Otherwise, it's been a pretty easy gun to shoot.