As stated above, velocity is the determining factor RE: "kinetic energy". But don't make the mistake of equating kinetic energy with killing or knock-down power.

The 9mm has alkways been loaded to the peak of its potential, but the recent advent ofvarious +P loadings in the .45 ACP place it far beyond anything a 9mm can do!

For example, one of my own .45 ACP handloads uses a 230-grain cast semi-wadcutter hollowpoint bullet at 1000 FPS andgives a muzzle energy of 510 FT/LB. I have even seen some .45 ACP "SUPER" ammo used in M1911A1's having ramped barrels that gave 1150 FPS with Hornady 230-grain XTP bullets. This load produces676 FT/LB, or nearly TWICE what you can get from any 9mm load.

Now, to avoid controversy, I am NOT going to assert that the .45 ACP is a better combat round than the 9mm! BUT, there is a reason why U.S. Special Operations forces are today buying specially made custom M1911A1-type .45 ACP handguns to replace the 9mm's they were using. And it is not just to complicate logistics problems....