The Hydra-Shock is just a more efficient form of a hollow point. By having a center post in the cavity the hydrodynamic force ensures more reliable opening of the tip. The Air Marshals use frangible bullets. Frangible bullets are basically sintered plastic and metal powder that breaks up whenever it hits a target. For really cool Hydrodynamic fun and guns look up Lehigh Defense Penetrator or their Cavitators.
