my 50 T/C firehawk using old TC maxi-hunters with 100 grs of 3f black powder topped wih a 3X9X40 Tasco will group 1" at 100 yds. This is old stuff compared to what's available now. A musket cap provides the fire.
Sometimes what's behind the trigger makes more of an impact on accuracy than what's being pushed down the barrel. Every rifle will tell you what load/bullet combination shoots best, you just need to find it.