Minie balls will not shoot well with heavy powder charges unless they are made with very thick skirts. With a thin skirt, the heavy powder charge expands the skirt to way over bore diameter as soon as it leaves the muzzle, and accuracy as well as ballistics are ruined. That's why the Army service charge with the 535-grain Minie during the Civil War was 60 grains - MV around 900 FPS. They still smashed the hell out of any living thing they hit -people and horses equally! To work well with heavier charges, the skirt has to be about as thick as those on the hollow-based version of the Buffalo Bullets.