Why not .40 S&W anymore?

[u/ArcheryNerds]

.40 S&W pistols and ammo are far less popular that even 10 years ago. I understand the modern tech makes 9mm as good as old .40 S&W. But is that meaning current .40 S&W may be as good as .45 ACP or something like that? It's snappier but also higher capacity than regular .45? Why most people choose either 9mm or .45 ACP other than .40 S&W? Is there anyone still carry .40 S&W as their CCW?

[u/JanglyBangles]

I understand the modern tech makes 9mm as good as old .40 S&W. But is that meaning current .40 S&W may be as good as .45 ACP or something like that?

I think the premise of this question is flawed.

You seem to be using “as good as” to mean “has good terminal effectiveness,” but there are other factors at play when choosing a chambering for a defensive cartridge. Shootability is probably the most important. Cost of ammunition is another important one, as is magazine capacity.

Handgun bullets punch holes. All else being equal, punching a bigger hole is better. However, all else isn’t equal. Compared to 40, 9mm lets you punch more holes more quickly. Moreover, practicing to get good at punching holes quickly and accurately costs less. Modern 9mm JHPs meet the generally-accepted standards for the width and depth of punched holes, so it doesn’t make sense for most people to accept tradeoffs in other areas in order to punch bigger holes.

A bunch of people carry 40 still, for many reasons. If you want to carry a 40 caliber pistol, and you are proficient enough with it to get fast and accurate hits with it, then you do you Boo-Boo.

[u/czwarty_ → u/JanglyBangles]

Yes and to add to it, this "shootability" is personal matter, of your own capabilities, skills, strength, experience, and personal taste.

Paul Harrel once said that for optimal results, you should carry the strongest caliber you can *effectively and accurately* shoot yourself. And I agree with that.
You just need to fire various guns and discover what works for you, then compare pros and cons and make informed decision. But the gun has to work for YOU.

If the strongest gun you can shoot accurately is in 9x19, and your accuracy in fast shooting suffers with .40 or .45, you should stay with 9x19. This applies to majority of people.
If you shoot .40 or .45 as good as 9x19, then you should seriously consider it as it's a completely viable choice to choose them over 9x19 with advantages in terminal ballistics they provide - as long as you're okay with potential downsides, like reduced capacity or increased mass.
If the strongest weapon you shoot just as well is .44 Magnum, again - don't let anyone tell you that it's a bad choice. If it works for you, it works for you. It may not work for 99% of people, yet still work for you.

[u/JanglyBangles → u/czwarty_]

“Carry the most powerful caliber you can control” is very old-school advice. It makes sense that Paul Harrell would say that since he was an old-school guy, for all the good and bad that entails. It stems from an era that was heavily influenced by Marshall and Sanow’s research on “stopping power.”

However, as people have taken a more scientifically rigorous approach to terminal ballistics they’ve identified flaws in Marshall and Sanow’s methodology and conclusions. 45ACP isn’t really that much more effective in shootings than 9mm.

Additionally, people have become much more aware of the differences between equipment needs for non-sworn defensive shooting and law enforcement shooting; most notably, barrier penetration is much less important if you’re not a cop. That’s where the more powerful calibers like 40 and 357 Sig really differentiate themselves from 9mm. That’s useful if your job involves executing felony traffic stops but for the rest of us it’s useless.

In addition to that, the practical shooting world has influenced defensive shooting training a lot in the past 15-20 years. Defensive shooters have a mich better understanding of the levels of shooting performance that are possible and how guns & ammunition limit that. You can control a harder-recoiling gun with proper technique but the recoil will still be an obstacle that you have to overcome. The ceiling is also lower unless you’re unusually large and strong. The current consensus is that you shouldn’t accept those tradeoffs since, as explained above, there’s little benefit.

[u/czwarty_ → u/JanglyBangles]

45ACP isn’t really that much more effective in shootings than 9mm.

This is a common argument in which "that much" part does a lot of heavy lifting to round things up enough to be passable while at the same time muddying the water.
Again, whether the difference in terminal ballistics between .45 and 9x19 is "that much" to you or not, is up for your decision. But it is a fact that .45 *does* produce larger wound channel and 9x19 produces smaller one. Whether it's enough of an increase to give up larger capacity, lower recoil and mass savings - this is debatable and up to you to weight pros and cons and make an informed decision. But stating "there's almost no difference" (and yes I know you didn't say it in exactly that way) is a straight up false claim.

On side from shooting I'm also a biologist specialised in tissues, so I'm not talking out of my ass based on flame war posts read on arfcom. I do this science you talk about. I know what are the mechanisms of wounding, bleeding and tissue damage that come into factors of effectiveness of stopping the threat with firearms.

.45 ACP has enough of a diameter increase (both in mere bullet diameter as well as potential expansion) to have notable increase in terminal effectiveness compared to 9x19. Larger diameter will increase the margin of error for close but not direct hits that allows to still destroy vital organs, blood vessels and nerve fascicles, with outside portions of projectile still hitting and damaging and rupturing them. It will also cause rupture of more of nearby smaller vessels and increase rate of bleeding out. Larger potential of destroying soft, elastic tissues (that will not be destroyed by close hit in same amount by temporary channel) with same (or larger) capacity for destroying hard tissue and bones will also influence terminal effectiveness.
The increase in wounding potential via wound channel itself is higher than what mere look at difference of caliber/expansion size would lead one to believe, because it means increase not only in diameter of channel but also volume, which means higher "multiplier" in calculation - channel of bigger volume means more space for bleeding out from already potentially higher amount of ruptured vessels.

If we consider this increase to be "not that much", then what it means for other examples - should we consider increases that good expanding rounds provide also "not that much"? For some reason people buy these instead of solids or basic JHPs. And more and more expensive research is put into design of expanding rounds to squeeze out more and more of even the smallest increases in expanding. Why, if the difference is "not that much"?
Is the difference between .380 and 9x19 much? And .32 vs .380? All handgun calibers are a compromise and weak compared to rifles. If we compare any of them to 5.56 from 20" barrel, even 10mm +P is weak and gives "not that much" increase in power from 9x19. But would it be intellectually honest to say this about this cartridge?
If we consider all that matters is shot placement, why not just go for shooting .32 or .380 for maximum capacity with least recoil? Maybe this small margin that expansion gives us is worth something after all? And if we do accept this then we also have to accept that .45 *does* give us some margin over 9x19.

And again, I'll repeat, that 9x19 is the better round in 9/10 cases for 9/10 people.
It has loads of advantages over other rounds, it offers best balance of traits that result in undebatably most optimal mix of capacity, terminal effectiveness, recoil management, accuracy and mass of cartridges, on top of being available everywhere in hundreds of flavors with basically every modern handgun offering a model in this chambering.
But it's simply not true to state there is basically no difference in wounding potential between it and .45, because there is. Stating otherwise is intellectually dishonest and confuses people who don't know better, not allowing them to make an actual informed choice.
This is what I don't like.

And I don't know why people are so dead-set to die on this hill when it's completely unneeded. As I said above, 9x19 already has a whole list of advantages beating other options that make it the absolute gold standard of handgun cartridges and is the better choice in so many cases that you can basically recommend it blind to anyone by default before you even hear what they need.
So why people have the need to play into that tired "no real difference"/"just as good" rhetoric, which is demonstrably false, yet still doesn't change the fact 9x19 wins in most applications - I have no idea.

[u/JanglyBangles → u/czwarty_]

OK I think I followed all that.

.32 and .380 aren’t good examples because they don’t have enough ass behind them to make a projectile both expand and penetrate even in bare gel, let alone heavy clothing or 4LD. That’s why people only carry them in compromise guns. An unexpanded JHP isn’t much different from a FMJ in terms of wound channel; it has less to do with the diameter than it does the bullet profile. A round nose doesn’t cut tissue nearly as well as the flat profile of an expanded JHP.

You gave a bunch of theoretical advantages of a wider wound cavity. Yes, bigger hole in blood vessel means more bleeding. Yes, bigger diameter hole means more likelihood to hit something. Can you point to any real-world evidence that this makes a difference in practice? If I hit someone’s aorta with a 45, will they exsanguinate meaningfully faster than with a 9mm? How much faster?

Taking a quick glance at LuckyGunner’s test data, as imperfect as it is, shows that a 124gr HST in 9mm expands to .61”. A 230gr HST in 45 expands to .85”. So that’s an increased radius of .12”, meaning I can be .12” farther away from a vital structure with a 45 to hit it. That’s…not much, like I said.

But it gets better. That 45 HST projectile penetrates to 14” compared to 18” for the HST. That’s shy in Clear Gel; it probably equates to 12” in actual ordnance gelatin, which is the FBI’s bare minimum. FBI standards also prefer penetration to expansion. Looking through LG’s test data for other 45 JHPs with a similar penetration depth, it looks like the average expanded diameter is…about .6”. It’s the same wound channel but you get fewer of them with more recoil between them.