Both types of round use the same bullet types, which are full metal jacket or jacketed hollow point. .40 cal rounds have greater velocity and greater minimum energy, but .45 rounds usually hit harder and have higher maximum energy. .40 rounds are easier to be more accurate with at long ranges with, although both are great at short range. .40 cal rounds also have less recoil. Overall, they’re fairly similar in many respects, although .40 cal rounds are a little more versatile and easier for beginners. They’re both worthwhile and one is not really “better” all in all than the other.