[mcguyver]

A steel or tungsten core round is designed to penetrate body armour, because it transfers it's energy to a smaller area and does not deform. Even if it's mass is less than a solid lead or jacketed round. This principal has been used for decades, and is well proven.

Deformation does not necessarily mean more injury or damage, especially to hard targets. Deformation of a real gun round inside tissue may cause more damage, depending on velocity and energy, and also fragmentation of the round.

I discount the Levante Labs study out of hand because they make the assertion that a deforming BB causes more damage. Now, they couldn't convince me that water is wet, I'll look elsewhere for a study that doesn't get it so blatantly wrong.