Actually that law is an ancient one on the books. It was originally put in place to prevent farmers from using old military .303 springfields to bang away at ground hogs and fox. Alot of surplus ammo was hardball at one time and they just didn't want to have bullets bouncing all over the countryside ripping through barns, kids and cattle. Modern Varmint hunters use the normal .22 centerfires mostly and they are all perfectly legal. I haven't varmint hunted in years so the smallest caliber in my present arsenal is a .25-06 thats all. If I decide I like doingh this I would likely pickup a .22-250.