I'd like to respectfully disagree with you Rebel Hog.

The 9mm Luger has a nominal bore diameter of .355" for jacketed bullets. The .40S&W's nominal bore is .400", for a difference of .045", which is significant. The .40S&W is obviously larger diameter, but they both fit in the same size magazines, with the 9mm having a few more rounds capacity in a given sized magazine (now that the retarded AWB has expired and full capacity mags are legal again).

To answer Bucky's question about "knockdown power." With premium defensive JHP loads, both are very similar with the .40S&W having a slight advantage. Accuracy for both is more dependant on the gun than the cartridge. The .40S&W has a bit more recoil, but generally less than the .45ACP in my experience.

Mike