I tried them years ago. Accuracy was mediocre at best, worse than round ball. Nothing--playing with diameter (matching it to bore diameter), etc--did nothing to improve accuracy. Since I was winning matches with round ball, I gave up on minies in the 24 gauge.
Then I got a wild hair and thought maybe accuracy would be better in a larger bore. It was, but not by much. In the .69 caliber musket I tried I used an original mould that had more of the weight concentrated in the nose. Shifting the center of gravity forward appeared to make it perform like a shuttlecock rather than a book thrown across the room. . . but accuracy from a patched round ball was much better.