9mm vs 40: This Time It's Personal
If there's one thing that's been argued to death, it's 40 vs 9mm. However, people love to talk about it anyway so we're going to hash it out one more time!
Both of these rounds are intermediate, in that they aren't too powerful nor are they too big. Each has their dedicated fans. Both are definitely proven self-defense rounds and - along with .45 - are among the most popular carry rounds out there.
Which is better? Both have some strong points, but the reality is neither is so amazingly awesome at anything that you simply must have one or the other.
40 vs 9mm: The Smallest Big Bullet There Is
For those that missed the story, there's a reason why the whole 40 vs 9mm debate favored the bigger bullet for a time. It all starts back in 1986, during the Miami FBI shootout.
The quick version is a bunch of agents got in a shootout with a couple of guys and their handguns barely did anything. Most were carrying .38 Special or 9mm and things did not go well.
For a time, the FBI switched to handguns in 10mm, which satisfied their ballistic requirements. However, the recoil was a bit much for some agents, so they created a weaker load. Then they noticed the plus-size frame of the 10mm caused problems for a lot of agents - difficult to conceal, hard to operate single-handed with the bigger grip housing, etc. - and thus they had a quandary.
Smith and Wesson had an epiphany that the 10mm case could be trimmed back and hold the same powder charge as the FBI load, and the smaller case could be used in a 9mm frame.
It outclassed the 9mm in the ballistic testing of the day, and impressed enough law enforcement agencies over the years to get quite the following, as plenty still issue the .40 S&W.
What does it have going for it?
Basically, it's the smallest big bullet out there, packing a moderate amount of punch but more - at least in terms of kinetic energy - than 9mm, .380 and .38 Special. Since it fits in the 9mm frame, you can carry more rounds than 10mm or .45 ACP and certainly .357 Magnum and people with smaller hands can handle a .40 pistol pretty well. It isn't .22 LR, but it's easy enough to shoot for most people to hack it with a full size or compact.
So...that's why it's so popular. It's the smallest big bullet out there.
40 vs 9mm: The Little Guy Comes Roaring Back
Why is 9mm - or more formally, 9x19mm Parabellum - so popular? It's just big enough to be really useful, but not so big that it's hard to shoot. That's always been its appeal and certainly why the 40 vs 9mm debate these days so often is settled in favor of the 9mm round in terms of sales.
The 9mm was developed from the 7.65x21mm round (aka .30 Luger) by Georg Luger around the dawn of the 20th century by necking the case up to a .355-inch diameter (9mm) projectile to give it more "oomph."
So, what's good about 9mm? It's easy to shoot in terms of recoil and accuracy, so just about anyone can use a 9mm pistol - even a compact or subcompact - without too many issues and get competent relatively easily. Loaded properly, with a good hollow point, it's quite effective on hostile personnel.
However, what made the .40 a more viable alternative back in the day was that 9mm hollow points didn't have a good track record in terms of terminal performance, including in the 1986 Miami shootout. The revised FBI ballistic trials that started a year or two later confirmed as much.
That said, the quality of 9mm ammunition has caught up considerably. In fact, many 9mm loads equal or exceed that of .40 in terms of performance but also shootability these days, which is why the FBI dumped the .40 a couple years ago in favor of Glock 9mm pistols as their main duty weapon.
9mm vs 40: Wear And Tear
Another aspect of the whole 9mm vs 40 caliber war is the wear and tear on the gun. The idea goes that .40 S&W beats the heck out of pistols and beats the heck out of the shooter, which is why people that get into a .40 eventually drop it in lieu of a 9mm.
Here we have something with a basis in reality, but also some sweeping generalizations that should be addressed if a person is to have a good understanding of it.
Okay, so let's get started.
First, .40 S&W has slightly more chamber pressure, about 2,000 psi more than standard 9mm, which is not really enough to make too much of a difference.
There is the dreaded "Glock Kaboom," but that phenomenon has more to it than some realize. It tends to occur with Bubba's White Hot Handloads more so than factory ammunition.
Other contributing factors are weak brass (either cheap factory brass or brass weakened by multiple reloadings) and early Glock barrels, which didn't fully support the case head, which can lead to a case rupture with sufficient pressure.
In other words, .40 S&W does have more chamber pressure but it's barely any more than 9mm and merely contributes to the kaboom rather than causing it.
Why does the .40 have the reputation for punishing guns?
The typical .40 S&W projectiles are 155-grain, 165-grain and 180-grain. Typical muzzles velocities for these bullet weights are about 1150 to 1200 fps for most 155 grain loads, 1000 to 1100 fps for 165-gr loads, and just under 1000 fps for the 180-gr loads. In terms of energy, the .40 S&W typically adds an extra 50 ft-lbs as a baseline over 9mm.
So, why does that matter?
A heavier bullet going downrange takes more energy with it, which means more energy going in the opposite direction, which means the slide is cycling more violently than a 9mm pistol and especially with the lighter-for-caliber loads at higher velocities.
Unless the manufacturer or shooter has tuned the recoil spring by adjusting the spring rate, a more violent cycle means more wear and tear on the frame and the frame rails.
As to more of a beating on the shooter, remember that there are two aspects of recoil: recoil force, literally the amount of force generated by the gunshot - which can be quantified by mere calculation; it's literally a physics equation - and then you have felt recoil, which is what the shooter feels.
Any gun where the slide cycles more violently produces more felt recoil.
And in the modern era of light, compact polymer-framed pistols...the .40 S&W is going to bring the pain. Recoil force for a .40 pistol is roughly double that of a 9mm pistol of the same size and weight, after all. However, if you were to switch to a .40 S&W pistol with a metal frame, shoot the 180-grain bullets to tame the violent cycling (heavier bullets are slower and produce less muzzle energy) and add a stiffer recoil spring to slow down the slide...the shooter might have an easier time of it.
Not as easy as shooting 9mm, but if you felt like you HAD to shoot .40 S&W, that would tame it a bit.
40 vs 9mm: The Straight Dope
Okay, so how to REALLY settle 40 vs 9mm?
Go out and shoot a bit of both. Is there one you hit better with or prefer? Then get that. It's that simple.
We could sit here and compare ballistics all day, but that's not going to...okay, fine. We'll do it anyway.
A (one of them, anyway) standard 9mm load is a 115-grain projectile - ball or hollow point - going at about 1,200 feet per second (depending; it varies by manufacturer) and carrying about 350 foot-pounds (again, depending) of energy. The standard .40 S&W load is a 180-grain bullet at about 1,000 fps (again, depending) with about 400 ft-lbs. The difference in those terms is marginal. Expansion in gel tests usually reveals about the same; marginal advantage at best, which isn't enough to make a serious difference.
A couple decades ago, testing of the duty ammunition of the day showed some advantages to .40 S&W and the reduced-recoil 10mm loads. Deeper penetration, more reliable expansion and much better performance through barriers.
Today's duty ammunition? Not so much, and it's worth noting that the FBI - the agency which precipitated the development of .40 S&W - switched to (standard pressure, no less) 9mm 147-grain Speer Gold Dot as their duty load.
Pistol calibers are weak, and marksmanship is what wins gunfights. Even the mighty .44 Magnum doesn't have a perfect record as a man-stopper. No handgun cartridge does; there is no such thing as stopping power (well...maybe a .500 Smith and Wesson) in pistols.
Thus, we can say that neither 9mm nor .40 is a ballistic wunderkind. They are basically adequate. If you put 'em where they're supposed to go...they'll work.
However, it is also much easier for USPSA shooters to make major power factor with .40 S&W. There's plenty of 9mm loads that do too, but some are marginal; .40 S&W safely meets the standard, and a magazine holds more than a gun in 10mm or .45 ACP.
The major advantage of 9mm? It's cheaper, just as effective with quality ammunition and recoils less. So unless you're shooting Single Stack Major, there's no advantage to 10mm Lite.
That said, there are people that just want or prefer a .40, and that's totally fine. There are people who hate it, and that's fine too. The reality here is neither is really "better" than the other, but one has some advantages in terms of mass appeal. Neither is well-suited to any purpose beyond self-defense and target shooting. Neither is really a handloader's playground.
So...40 vs 9mm...the winner is whichever you like.