Marshall and Sanow's book, "Stopping Power" provides a lot of information on real world performance of various rounds and bullet types, but has been roundly criticized by many for its various methodology flaws. It makes for interesting reading, but don't believe all it says. Regardless of the caliber or bullet type, effectiveness depends on only two factors - adequate penetration and bullet placement. Meaning a brain or spine shot with a .25 ACP will do far more damage to a determined opponent than a pinky finger shot with a .44 Magnum.