I have one and so does my wife. They can be very accurate, approaching 1MOA, with the right load.
Harvester black 50 cal rifle 45 cal bullet sabots and 250 grain Hornady XTP or FTX bullets. Standard 209 primers work fine.
The green sabots with 44 cal (.429) bullets produce very poor accuracy in my rifles +4MOA
I prefer loose powder, Pyrodex or Triple 7, start with about 70 grains (by volume) and work up. At some point, probably between 80 and 90 grains. you will find the most accurate load.
Beyond a certain velocity accuracy will decline.
For ease of loading and best accuracy it helps to swab the bore every 2 or 3 shots. Alcohol swabs in foil packs from the pharmacy work great.
Internet wisdom will tell you the XTP bullets are no good at the velocities produced by a muzzle loader. I can tell you that I have shot over a dozen deer with them at ranges of 20 to over 200 yards and all have performed well.
Welcome to THR