I believe the Geneva convention prohibits it, not really sure why though. Also keep in mind war is not like hunting, they are not trying for the fastest kill or to be humane really. One of the reasons they switched to the 5.56 was because ammo was cheaper smaller and lighter, so they could carry more and it WOUNDED just as well. If you kill someone they fall and someone takes their place. If you wound them you take them out, plus a few others to take care of them.

Also FMJ's penetrate barriers and armor better.

Paul