I hear all the time the 45 vs 9mm, how the 9 doesn't have enough power, etc etc. My wife shoots a 9, and while I stick to the 45, feel the 9mm is adequate.
My eyes were opened when I wanted to test some new defensive rounds for expansion, got 5 milk jugs full of water, and shot my 45 hydrashoks into them. The 45 went through 4 of them, and made a slight hole in the back of the 4th one. The impact blew the tops off the jugs, but thats about it. Obviously, the water all drained out of it, and I retrieved my bullet. Later, we were shooting the "weak" 223, and I figured it would be fun to shoot at the empty milk jugs. First hit, the jug shot up about 8 feet in the air and split completely down the side, without a top on. Everybody knows that water is much harder to compress than air, so the empty jugs would take an extreme amount of energy to explode than the water filled ones.
It reminded me that handguns, even the larger calibers, are so far away from "weak" rifle cartridges. And it was freakin cool!