A 9mm (or .38 special) in the head beats a .45 in the body armor every time.
The “caliber must start with a .4 crowd” make a fallacious argument, because James Butler Hickok used .36 caliber Colt Navy revolvers.
That caliber was most effective in his hands, and his death was a result of his seating choice, not caliber.
The Army did not know that, and 15 years fighting the Moro only confused them more.
“At the time US troops were armed with either .30 caliber Krag or Springfield bolt-action rifles and .38 caliber double-action revolvers. While the .30 caliber rifles proved effective in stopping the attackers, the US troop’s handguns demonstrated an unnerving lack of stopping power, resulting in numerous reports of Moro warriors absorbing multiple pistol bullets while they continued to hack away at the Americans. Obviously the US troops’ morale suffered badly in this situation.
The combat pistol situation became so acute that old stocks of Model 1873 Colt revolvers in 45 caliber, many of which dated back to the Plains Indian Wars were returned to active service, where they quickly demonstrated a much better track record of stopping an attacker with one well-placed shot.
The battlefield experience against the Moros resulted in the famous Thompson-LeGarde tests by the US Military in 1904. In these tests a variety of military cartridges of the day were tested for their penetration, ‘stopping ability’ and energy transfer, using both live and dead cattle at the target medium. While somewhat subjective by modern standards, the tests resulted in an official recommendation “…that a bullet, which will have the shock effect and stopping effect at short ranges necessary for a military pistol or revolver, should have a caliber not less than .45.”