There is absolutely NOTHING wrong with the .40 S&W cartridge. However, I don't find the 9mm lacking either (personally), and 9mm holds more boo-lits, is cheaper to shoot, lighter recoil. So that's why I've only ever owned ONE .40 S&W ever. Now that I've learned that several .40's will work perfectly with 9mm with only a barrel swap (but recoil spring and magazine change seem rather prudent for self defense), I think I'll be changing my tune and buying .40's much more, and then pick up a 9mm conversion.
Good call on the Shield though, those are great little compact pistols.
