.177 cal will shoot bebbies also, 20 cal may be exclusive to sheridan and a bit harder to find pellets, 22 cal most popular and for small game a best choise. You can put a small scope on it and really have a nice accurate package. Just remember to be careful. My friend made the mistake of putting his thumb over the barrel end while pumping the air rifle. He did infact discharge a pellet through his thumb and a hospital visit. He should have put the pellet in last,with the safety on! Good luck and happy plinking.