This is what a .30 cal do to a penny @100 yard
http://docilekids.com/temp/7.62x54R-1%20Hole.jpg
Compare to a .22lr @100 yard.
http://pound.docilekids.com/
.22lr bends or crack (deflection) them.
Anyway, let me clarify my last post. Yes a .22lr can kill a person @100 yard but not with one shot. It will probably take a few shots to do it @100 yards. I honestly think without a doubt that a .22lr will not penetrate a human skull @100 yard.
Like the other poster said, the .22lr are use as a sniper weapon because of low flash and sound signature.