A .54 Renegade, my first ML, came w/ strict instructions to shoot PRB w/ 95 gr Pyrodex.
So I did. And after 10 shots or so my shoulder hurt; groups were OK but not great at 50 yds .
The day I decided to sell that rifle I took it out one last time but loaded w/ 75 gr instead. Groups tightened considerably as I recall and it was actually enjoyable to shoot.