The driving bands on REAL slugs are said to be in .005" increments of diameter.
That is because in muzzleloading there is no standard bore diameter.
Supposedly the smallest band (base) will lightly engrave, and each band engraves a bit deeper as you insert the bullet.
Soft lead does in fact obturate with black powder, so the REAL is to grab the rifling no matter your bore size.
I have shot 45acp bullets out of a muzzleloader, and they did stabilize, therefore I know they are obturating & grabbing the rifling.