.22 will do all you need. I use .25 on coyotes, shot placement is key. Know your gun and your limits. Pretty simple,if you do not have the proper shot, do not take it. Even a slow .22 crossman will take out about any varmint within 50yds. Some are tougher than others, if you are worried, study said animals anatomy a bit more. Bigger caliber is not always the answer, knowledge is.