Twist = 150 X D2/L
Where:
D = bullet diameter in inches
L= bullet length in inches
150 = a constant
This formula gives maximum length of a projectile at muzzleloader normal speeds.
For instance a .45 caliber 1-48 twist would shoot best with a projectile under .625 this could include a Patch round ball, a real bullet or a sabot-ed bullet that was short enough. If they are longer than the length that will stabilize you will lose accuracy and may even tumble if it way to long.
This changes with caliber for instance a 50 caliber 1 in 48 twist will take a bit longer bullet .75 and shorter.
I hope this helps you understand better. Lee