How Military Rifle Bullets Destroy Tissues

I read the news about the attempt on Khun Sondhi Limthongkul's life and the police said that there were several assault rifles (such as AK-47, M-16, and HK) used, so I went to do a bit of research on what the bullets fired from these rifles would do to a human being. I stumbled on the "Military rifle bullet wound patterns" article by the battlefield surgeon Martin L. Fackler.

You might also be interested in how fast these bullets move (at a few times the speed of sound.)

I also don't know why the assassins used many kinds of rifles.