A .22 Magnum will be plenty but a standard .22 LR round nose would take care of them if you hit them correctly. Stick with solid, preferably jacketed, rounds because hollow points often blow up on their fur and only injure them temporarily. Also, don't go for a body shot. They are mostly fur so if you do actually hit them, the bullet will have a hard time penetrating. That was the problem with my 17HMR hunting rounds on skunks. Too much kinetic energy in the bullet, too little momentum, especially for ballistic tips and hollow points. FMJ rounds were a totally different story, but I never used them for hunting for obvious reasons.