My dad shot a wounded deer in the head at point blank with a .40 S&W JHP, it didn't die, he had to shoot it again.
At another point the same thing happened, he shot this one with a 9mm, it died immediately. This subject has been beaten to death. Caliber doesn't matter, a bullet is still a hunk of metal tearing through you at 1000 feet per second.
If you rely only on a .45 to get the job done because of sheer size, you are going about it wrong.
President Reagan was hit with a .22, it didn't kill him, but it sure as heck incapacitated him.