Why Do People Still Argue About 9mm v. .45 ACP?

Ah, yes. The never ending debate about which is better: Coke or Pepsi  Star Wars or Star Trek  Kirk or Picard  Ford or Chevy  9mm or .45 ACP. Sam Hoober, writing at The Truth About Guns, thinks he has the answer. He begins by noting:

    What’s been relatively common knowledge for some time now is that it’s not really a binary choice. The typical gun owner won’t see much difference in accuracy or performance in any real world application.

    Today, you can get great ammunition in both calibers. Plenty of very good firearms that anyone would be proud to own and carry are available chambered for both rounds.

    It’s been well established that both are excellent choices for both personal protection and target work. Any ballistic advantage is incremental at best or only matters on paper instead of in real-word results (competitive shooting aside). As for “stopping power,” given good quality ammo, neither produces a wound much bigger than the other, nor is one more consistently fatal to bad guys.

    What’s known about gunfights involving handguns is that shot placement wins them much more than caliber will. They’re usually over after expending fewer than 10 rounds, so capacity doesn’t matter all that much either in most cases.

So the inference is that there really shouldn't be a debate because they are equally good and everyone should just get along. (Which is, in itself, an argument in favor of 9mm because it costs less, weighs less, and you can stuff more into a smaller package).

    So why the debate then? Hoober puts it down to three factors:

1. Because back in the day, before good quality hollow point bullet designs, it actually made a difference and (older) shooters just can't let it go;  
2. People are tribalist and if we see anyone different from us, even as to issues of taste, we believe that other person is wrong and needs to be corrected; and, 
3. As he expresses it, "[b]asically, people are fundamentally insecure. Someone believes or enjoys something that isn’t what we believe or like, so we must somehow prove that those other people are wrong, providing the validation we so desperately crave."

    Unfortunately for him, Hoober is wrong. Not about the three reasons why people argue about it--he's spot on in that regard--but in his assertion that the two rounds are ballistically indistinguishable now that we have good quality hollow-point ammunition. 

Left to right: 9mm, .40 S&W, 10mm, .45 ACP (Source)

    First, even with better bullets, there can still be quite a bit of variance in expansion. I would refer you to Lucky Gunner's ballistic tests of handgun defensive ammo. The best expansion for 9mm was .74 inches using Winchester 147 gr Ranger T-Series. The area of a circle with a .74 diameter is  .43 square inches. But that was actually quite exceptional expansion. I haven't crunched the numbers to get an average, but most of the ammo tested appears to fall between .5 and .6 inches in expansion. Assuming a .6 diameter, the area of the circle would be .28 square inches. 

    The best expansion among the .45 ACP was with Winchester 230 gr Ranger T-Series with an average expansion diameter of 1.00 inch! That would give an area of .78 square inches. The Winchester 230 gr Ranger T-Series +P was right up there at .99 inches. Again, this is exceptional, but where there was expansion (the low velocity of the .45 ACP sometimes results in little or no expansion) it was generally more than the 9mm, with quite a few in the roughly .6 to just over .8 range. Assuming a .8 expansion, the area is .50 square inches. 

    So, in short, you can get substantially more expansion from .45 ACP than even the best 9mm--nearly twice the frontal area, in fact.

    In this regard, I would observe a 2021 article from Massad Ayoob on "Is The .45 Obsolete?" which notes:

Speaking of fact, wound volume is still a “thing.” Assuming identical shot placement and wound track angles, the larger wound should have the greater incapacitating effect. Gunfighting expert Jeff Cooper had a different background than military combat surgeon and wound ballistics authority Martin Fackler, MD, FACS, but each came to the same conclusion on one thing: assuming the same bullet configuration, a .45 slug could cut a 60% larger wound channel than a 9mm.

A bit further into the article and Ayoob explains:

    The fact is that a .45 bullet has “more lead to spread.” True enough, today’s best 9mm is expanding as well as yesteryear’s .45 ACP jacketed hollow points (JHP), and perhaps more consistently.

    However, I’ve never seen a 9mm bullet expand to a full 1″ in diameter in living tissue. I’ve seen that with two .45 ACP loads: the old Speer 200-gr. driven at +P velocity from a 4.25” barrel, and the current Federal HST 230-gr. +P at 950 feet per second from a 5” barrel.

    And if the bullet doesn’t expand … Heavy clothing and other barriers have been known to clog the hollow cavities of even high-tech JHP bullets, bringing us back to full metal jacket “hardball” performance. See the comments of Cooper, Fackler and Schwartz, above. If you’re in a frigid clime and your opponent is likely to be heavily clad, when your JHP turns into FMJ you probably want it to be a big FMJ, and that favors .45 ACP.

    Second, even with good quality hollow-point, you may still get little or no expansion under certain circumstances. In those cases, the .45 ACP will probably still give you a wound channel that is .1 inches larger in diameter than the 9mm (.355 inches). 

    Third, the recoil and recoil impulse is different between the two. Some people have no issues with the recoil from the .45 ACP, but others might. My wife, for instance, can tolerate the recoil from 9mm, but finds the .45 ACP too unpleasant to shoot at all.

    Fourth, the differing bullet weights and pressures give different velocities, resulting in the 9mm typically shooting flatter than the .45 ACP. It may not make a difference at typical handgun distances, but can if you push the ranges out farther. This becomes even more apparent when using light weight (90 or 95 grain) bullets.

    Fifth, because of the lower velocities in typical .45 ACP ammunition--often already below the speed of sound--it makes a better suppressor host. 

    In the end, I have to agree with Hoober that shot placement is more important than caliber in a gun fight, and the difference in magazine capacity probably will not be dispositive. But neither are the two rounds ballistically indistinguishable. So, for some people, there is still reason to argue for one over the other for particular purposes.

    I will add that I grew up shooting 9mm (my father didn't have a .45) and have always preferred 9mm even back before the creation of the modern hollow points, when all the experts were saying that .45 ACP was the only reasonable choice for self-defense. So I'm not exactly what you would call a .45 ACP fan boy. But I have learned to appreciate the .45 ACP, and the 1911 pistol, as I've gained experience with them. Thus, if I'm not carrying a revolver or opting for a smaller .380, I am carrying a 9mm. I also much prefer the 9mm for shooting for fun or practice. But I have shifted to .45 ACP for my nightstand gun.