I use Federal 209 primers, which I believe is what the manufacturer recommends. Even so, I've had a few failures to fire, but most of them were probably my fault.

Blackhorn does require the bullet and sabot to be seated tightly. It's hard to do with those pistols since there isn't a buttstock to place on the ground to give some leverage. Just try to press that ramrod down as hard as you possibly can.

Speaking of Blackhorn, it seems like 80 grains of it behind a 200-250 grain saboted bullet is the sweet spot in the Optima. Mine would do about 1-1.5" groups at 100 yards, and it still has power to spare at that distance.