What Brasso4 said. When i was in my departments ordnance unit we had an ammo rep from a major manufacturer put on a demonstration. We fired all the major brands into gelatin using the FBI protocols. All the ammo penetrated about the same depth and expanded to approximately the same size. The Rep thought this was cool. I asked him why would an agency pick one caliber over another if the ammo performance was similar. He stammered a second but he offered no real answer. FWIW, I want ammo that maximizes performance in that particular caliber. I don't want a 45 round that penetrates the same as a 9mm. I want a 45 load that gets the most out of a 45. If the performance is maximized for the particular caliber, then i would pick the biggest one i could handle.