What's a good gun for Varmit hunting (coyote, bobcat,fox, etc)?

Me and my friend are going varmit hunting this august and he is going to buy a rifle. He wants something like a SU-16A. I'm trying to convince him to buy a .223 bolt action rifle. Something like the Savage Varmiter, and he just doesn't get why the a bolt action would be better. What rifle do you recommend and should he get a bolt or semi-auto?