One thing I forgot to say... there probably are two sets of velocities... 1. being the velocities that the petals will performed as designed and 2. if the bullet is at a reduced velocity the nose still opens to some degree, it just will not have enough velocity to break them off and allow them fly outward. With a reduced velocity and the nose opening partially the bullet then operates somewhat like a normal mushrooming bullet.

does that make some sense?

pete