if you go back to the original post and the question of why the army from a 38 to a 45, you have to look at the original situation.
The US Military Had just faced the 7X57 mausers of the spanish in the War with Spain in both cuba and in the philipines, realizing the superiority of the new rifles, work was to proceed on modernising the weapons of the US. The Krag Rifle was adopted and the .38 Colt was introduced, replacing the SAA colt and the other various 45 cal revolvers. As soon as the spanish had been forced out of the Philipines, a war of insurgency broke out among the philipine people against the US in there attempts to earn independence and self autonomy. In facing the philipino tribesmen, the US military were often facing an opponent who was drugged up, psyched up and in many cases in a nearly crazed state who would attack and fight until he was fully broken down, The Army discovered that the 38 colt did not have enough punch to stop the fight quickly enough. The M1889/1995 revolvers were not known as reliable guns to begin with, and firing a 148 grain LRN at about 750FPS It was not a reliable fight stopper. There were troops in the Philipines still had the Colt SAA as the issued sidearm and these units found that one 250 LRN at 875 to 900 FPS was a huge improvement over a a couple of 148's at 750. With this improvement came confidence in the rounds ability to stop a charging Moro, and with the confidence came more care in aiming and thus even higher success. So a call was made to the army HG for more .45's which were called "man stoppers". As many of the Colt SAA's in Gov't stocks were older and needed to be retired, a call went out for a new pistol to fire a .45 cal 230 to 250 grain slug at or about 835 FPS. JMB took up the challenge and modified a model 1900 auto pistol to hold a new round developed by himself and winchester. Called the Model 1905, the new autoloader and round were not accepted and further testing and competition between UMC and winchester finally ended up with the round and the pistol we know as the 45 ACP and the 1911 Colt pistol. if you wan tot do more look here or google the moro war.