I never find myself using hollow points because most of the damage of an HP round seems to mostly affect the outer shell of the craft and not the juicy internals. What I propose is a penetration coefficient for HP rounds where you can set how much the shell penetrates before acting like a hollow point round. A range between 0% and 40% seems reasonable.
Ie if I have a 10000 damage hollow point round, and I set the penetration coefficient to 25%, then it will penetrate like a hard tip round for 2500 kinetic damage, then propagate out like a HP round for 7500 impact damage when that 2500 kinetic damage is used up.
AP values would be different for kinetic and impact.
HP bullets that would ricochet if they are AP will apply only the HP part of the damage, and not the kinetic damage.