Brass Fetcher,a website devoted to scientific,repeatable and reputable ballistic tests,went "there". Yep. Its .45acp vs. 9x19 Parabellum time again! BUT before anyone gets their knickers in a twist,the now oft-repeated internet caveat should be mentioned: Whats more important then caliber is your ability with your particular gun. With handguns chambered in service cartridges of all calibers from .32acp (YES,.32acp was used as a "service" cartridge,being prominently used in the Walther PP and PPK by police in Europe primarily in Germany; Patton even famously fired at a stuka with his colt pocket automatic chambered in it!) to 10mm,the most conclusive thing has been the anomalous performance recorded across the board when used against human adversaries. (As a side note,the .22lr was even used as a service cartridge by the Mossad- with some effectiveness,too.) According to one prominent web blogger on firearms,Stephen A. Camp: "If a 150 pound deer can be shot through the heart with a .30-06 180-gr. expanding bullet at 2700 ft/sec and keep moving, should we expect that a 200 pound human hit with a 180-gr. expanding forty-caliber bullet at 975 ft/sec to be instantly incapacitated?" You should not rely on your handgun caliber selection to even give you a slight advantage. You should rely on your ability to get good,repeat hits with whatever gun/caliber you choose. This post is strictly for informational purposes only,and not intended to ignite a flame war. Of particular importance,IMHO,are the "bone tests" of both of these calibers.