Having fired the Beretta 9mm, a Glock 0.40 S&W and the 0.45 ACP 1911 quite a bit, I can say that 9mm has a lot of advantages over the 0.45. Shooting the 9mm is like shooting a 0.22 rifle, you can pull the trigger very fast and punch a nice hole in the head at 15+ yards. Whereas the 0.45, with no form or porting/muzzle brake, requires a lot of recovery time between trigger pulls to be accurate. While standing duty, we carried three magazines: 3 x 7 0.45 or 3 x 15 9mm. That's a big difference in number shots and sailors don't train very much, so the 9mm was a much more practical choice. The key with the 0.45, is that if you are used to the recoil and can aim well, you only need one hit per target pretty much no matter where you hit if you have any of the good hollow points. I use Federal Hydrashock out of habit, though I am sure newer, better rounds have been developed since I started carrying in 1997.
0.40 S&W seems like the magic happy spot. Almost as easy to shoot as the 9mm and with a decent velocity for accuracy and penetration, but almost as heavy a hitter as the 0.45. Maybe I should get a 1911 chambered in 0.40 S&W? I am an old dog and have loved 0.45 1911s since I was very young. It's not like I have ever gotten in a shooting situation, but if I ever do, I am pretty sure the 0.45 ACP will be adequate for me in most situations. For hobby purposes, I see no reason to give up the 0.45 other than to go to a cheaper caliber like 0.22.
