Yes, I know that the .40 S&W, occasionally known as the .40 Short & Weak, has been hailed as the most lethal round from a hand-held weapon since the RPG, packing the pure stopping power of a cement truck filled with molden lead. You can read the adulatory entry in the Wikipedia or, if you've got some time on your hands, you can read all 11,400 entries in the Google search "stopping power comparison between 9mm and .40 S&W." Yes indeedy, the power of a .45 ACP with the capacity of a Wonder-9! Better than peanut butter and jelly in the same jar!
Okay, so no sane person, given any sort of choice, would opt for a 9mm or a .45 ACP when he or she could have this amazing miracle round.
I've certainly shot enough .40...I competed in USPSA with an STI EDGE in .40, the absolute baseline gun for USPSA Limited competition, and it rocked. I shot IDPA with a .40 High Power . When the first little bitty .40s came out — as it happens, it was a Star FireStar M-40 — I shelled out far too much money for a Spanish gun, sent it to gunsmith Mike LaRocca, who bitched mightily but did a flawless action job on the gun, whined until Tim Wegner at Blade-Tech made me an IWB for the little gun. I carried it for several years and put a couple of thousand rounds through it before I changed first to an STI LS-9 9mm, then the SIG P225 in 9mm.
Now why would I voluntarily "downgrade" myself from this Jedi knight light saber of a round to a plain vanilla 9mm, which as everyone who reads gun magazines knows is only slightly more efficient than a spitball from a 13-year-old schoolgirl?
Okey-dokey...let me step you through it:
1) Sophisticated computer-aided bullet design has drastically narrowed the gap between the handgun cartridges. To a large extent, the drastic differences in "handgun stopping power" have involved comparisons with ball ammo.So anyhow, shoot what you want to and what you can shoot well. Your experiences may differ from mine, and you're every bit as correct as me. Not as handsome and scintillating, of course...
2) I'm not a cop nor in the military; I can choose to carry any bullet I want. The military has numerous constraints on their handgun ammo, and so does law enforcement. One of those big constraints is price. I buy the round I'm the most comfortable with — Hornady TAPS — and, yes, it's more expensive than the average bear.
3) My experience has been that I can deliver more accurate rounds faster with either a 9mm or a .45 ACP than with a .40 in the equivalent small frame semiauto. I believe this has to do with the recoil impulse of the .40, which is sharp and nasty in a little gun...and I've shot a lot of them.
4) The .40 S&W has a spooky pressure curve, especially related to overall case length. If the bullet is driven back into the case, pressures can spike sharply. I don't like high pressure surprises, no matter how remote the chance.
5) I HATED developing loads for the .40...it seemed to me to be a far more finicky beastie than the .45 ACP (or the 9mm, which I typically don't reload). When I finally got a load that rocked in my EDGE, the High Power flatly hated it. The loads that ran well and were super accurate in the H-P jammed the EDGE up. The loads that worked best in my single stack STI Trojan sucked in everything else. My experience with the .45 ACP and the revolver rounds found much less "swing" with the same loads in similar guns. My baseline .45 loads work pretty well in everything.
6) There's the undefinable "take it to the range" factor...I always take an additional gun (or guns) to the range no matter what I'm there for, just to do a little practice or plinking when I'm done with my main shooting. I found that the .40s stayed in the safe. Hmmmmmmm...David Caruso would call that a "clue."
7) On travels, I have on occasion had to buy ammo from Wally-World or the random K-Mart...in those cases where I know I have to buy ammo, I invariably carry a .45 ACP and buy 230-grain FMJ ball. .45 ball works.
8) Finally, "stopping power" is wildly secondary to bullet placement. Let me say that again...in a handgun round, bullet placement is everything. What I want in a carry gun is the absolute knowledge that I can deliver the shot with that gun and that load. The little .40s required more from me than the 9mms and the .45 ACPs.