bmc1891 said:
No kidding. but at CBQ distances, is a rifle cartridge necessary? Plus, like I said, you'd have commonality with your sidearm, which means one type of ammo.
Like squeeze said... body armor and unknown threat.
And if I'm doing it right, the .45 ACP delivers more ft-lbs of energy at the muzzle than the .223 Remington. I got the charts here (if I'm reading this stuff wrong, let me know please!):
http://www.exteriorballistics.com/ebexplained/index.cfm
Let's look at the Winchester Q3131A 5.56mm load, which is a M193 load (and also the load I like to use in my AR-15s

)
Muzzle: 3270 fps, 1306 lbs-ft
Now let's look at the Winchester RA45T Ranger-T .45 load, something you won't see in the military, but it's a very well respected JHP. It has more energy than a FMJ load.
Muzzle: 885 fps, 400 lbs-ft
As you can see, they aren't even close.
And as to Squeeze's post: correct me if I'm wrong, but we're only officially allowed to use ball, FMJ ammo in the military because of international agreement correct?
You can use JHP on terrorists as they are not signatories of the Hague Convention. It is also allowed to "prevent overpenetration in the event of hostages present" or whatnot.