Find a round that shoots well in your handgun and learn to shoot it. Most modern controlled-expansion 9mm Parabellum rounds will do the job if you put it where it needs to go, especially double taps. To my knowledge, no one has proved conclusively that 124 gr. bullets perform better or worst than 115 grain bullets in actual shooting situations. Personally, I prefer 115 and 124 gr. hollowpoints over subsonic 147 grain bullets, but that's just my preference. Rule #1 in a gunfight is have a gun. Rule #2 is have the most powerful gun you can handle. If you are unable at anytime to obey Rule #2, always obey Rule #1: HAVE A GUN, on account no one likes to be shot at, whether it's with a .454 or a .22...