All my pistols are 9mm , thats for two main reasons , more rounds , and so that my girl can use them easily . I dont get into arguments about cal, except to bash the .223 baby bullet , but thats another topic . Point is , have something , Considering most home defense shootings happen at ranges of less than 20 ft . , they are almost literally in your face …………….9mm will do just fine , so will most other cals .One cal , that is a proven man killer , that is not real common in the US , but its worth mentioning , the Soviet 7.62×25 is a very fast and hard hitting round . The pistols that shoot this are inexpensive surplus weapons , and you can get surplus ammo as well . Its a battle proven round .