I read a story a few years ago about a Blackwater contractor who got off a lucky shot from an extremely long distance that hit a running Iraqi in the ass cheek, and it was an instant kill shot. It tore up the guy's entire lower stomach.
Naturally, they wouldn't let our guys use them anymore, as that just wouldn't be "fair".
Use of expanding ammo in personal weapons is banned by the Geneva Convention.
Typically anyone captured with expanding bullets is summarily executed, a practice I thoroughly support.