From the wiki article on the .45 ACP round:
"Even in its non-expanding full metal jacket (FMJ) version, the .45 ACP cartridge has a reputation for effectiveness against human targets because its large diameter creates a deep and substantial permanent wound channel, although some writers, such as the published work of Marshall and Sanow, have cast the reputation of .45 ACP being the "best" at this task into doubt. Marshall & Sanow's work, while receiving heavy criticism from Dr. Fackler, still show the .45 ACP, loaded with the best hollowpoint bullets, to be a "one shot kill", somewhat better than the 9mm Luger, equal with the .40 S&W, and only a few percentage points behind the "King" of the Marshall and Sanow study - the .357 Magnum. It does not, however, match up to the 9mm Luger, the .40 S&W or the .357 Magnum without the best hollowpoint bullets. The .45 ACP averages 78.5% "one shot kill" while the 9mm Luger averages 87%, the .357 Magnum averages 89.5% with the .40 S&W on top with 91.5% average "one shot kill". The .45 ACP remains one of the top handgun cartridges for stopping power."