There is, however, another benefit you could get of theese kind of bullets:
Put some anastetics into the bullet, medium pressure (cause after the explosion you don't want the bullets to cause too much damage). Still the bullet would be reshaped by the kinetical energy of pertifying the amour (if there is doubt the energy would not be not enough, the bullets tip could be covered in a flamable substance, like the tip of a match, even without having to fear a bad fight behavior too much.
The pressure of the liquid still will cause to explode the bullet and expand into the opponent body, after the heat causes the bullet to transform itself. While the bullet itself doesn't do much of a harm (still it is a bullet and there will be a shooting wound, probably a empty shell inside the body, though), the anastetics will stun large parts of the body. As long as the anastetics work, these parts won't be able to sensor, causing the opponent not to be able to move, stand, grab or use a device, since there would be no nerval feedback on this actions. He would be paralized (at least partially if there is a bad hit).
The worst paralizing effect would take effort if the opponent is hit in the torso (since it is mostly free space, so the anastetics would be able to spread wide inside the body). Hitting the chest could probably cause one of the lungs to malfunction, what would stun you for good, or causing a heart attack (waht would end you for good). Hitting one limb would probably only take out this particuar limb. Hitting the head would turn out bad (well, you'd to have a bullet shot into the head), but I honestly could not predict how bad the paralizing effect would be (might be fatal, too).