A police officer's recommendation for self-defense against an attacker hopped-up on the latest generation of synthetic marijuana generated some discussion. I was struck by how many of the comments ignored the point of the police officer's advice, which was:
... typical deep-concealment (i.e. small, lightweight) pocket revolvers and pistols are simply not adequate to deal with people under the influence of this stuff. His personal opinion was that .32 ACP, .380 ACP, .38 Special, and even 9mm. Luger or .357 Magnum rounds, if fired from smaller weapons whose barrels aren't sufficiently long to give high velocity and promote bullet expansion, are not going to get the job done against a hopped-up addict who won't even realize he's been shot.
His advice was specifically limited to small, deep-concealment firearms, the kind of thing many of us drop into our pockets rather than worry about putting on a holster and carrying a full-size firearm. It was not intended to discuss the latter at all. However, a number of commenters ignored that caveat, and responded as if he were making a general statement about all defensive handguns and ammunition. That was not the case.
Let me offer a few observations, based on approximately 18 years in military and civilian combat situations, unrest, insurgency and instability in Africa. I think the hard-won lessons I learned there apply to just about anything we're likely to encounter in the USA. Those with actual real-world experience (rather than just theoretical knowledge) of the field are invited to respond in Comments.
1. Bullet performance against people can be generally predicted from its performance against similar-sized animals.
If a round, and/or the firearm(s) that fire(s) it, do well against animals of equivalent size, weight, etc. to human beings, it's likely to do well against the latter. If a round doesn't deliver good performance against deer, or antelope, or hogs, or whatever, in the 150-250 pound weight class, what makes you think it'll improve when used against people in that weight category? If animals don't drop to it, people probably won't either.
2. Absent a central nervous system hit, blood loss and broken bones are the main incapacitating factors in both hunting and self-defense.
When hunting, a hit in the target's brain or spinal cord is likely to prove decisive, right there. However, they're hard to hit (particularly when the target is moving or at longer range), and they're also well armored by bone structures (the skull and/or the spinal column). If they aren't hit, the object becomes to stop the animal moving (and thereby either getting away or attacking you), and/or to cause the maximum possible blood loss, which will lead to incapacitation sooner rather than later. To stop an animal moving, you have to break the bone structures that allow it to move; this usually involves shooting through the shoulders or hips. Again, those targets are harder to hit, and may not be available at all target angles. Therefore, one tries to make as big a hole as possible in or near vital organs, so that blood loss will be rapid, depriving the animal of the oxygen its vital organs need to continue functioning. Shooting through an animal is a preferred solution in Africa, where two holes are regarded as better than one for the purposes of blood loss.
Again, apply this to human beings. If you take out a major bone in the legs or hips, it's likely to at least slow down an attacker, no matter how hopped-up on drugs he or she may be. If you inflict rapid blood loss upon them, that will also produce a reasonably rapid change of status. Both objectives are more likely to be achieved by larger, heavier bullets than by smaller, lighter ones. Modern ammunition, with its more technologically advanced design, can make up for smaller bullet size to some extent (as evidenced by the resurgence of the 9mm. round in police work). However, if a smaller bullet fails to expand or drive deep enough, it still won't get the job done, whereas a non-expanding bigger bullet is still just plain bigger!
If you apply those considerations to your selection of handgun calibers and cartridges, it simplifies matters enormously. It was my experience, during the 1970's through the 1990's, that larger, heavier bullets were much more effective than smaller, lighter ones. I don't care about theory; I'm talking about actual practice. In Africa, if a bullet proved effective against antelope such as bushbuck, impala, nyala, sitatunga and springbok, it generally worked well against people too. In the USA, where my hunting experience is much more limited, I'd presume the same applies to bullets that work against black-tailed deer, mule deer, pronghorn and white-tailed deer. In all cases, we're talking about bullets that bring down a running deer within a reasonably short distance, allowing the hunter to recover it easily. We're not talking about shooting it in the ear with a .22LR solid at spitting distance (although that's certainly effective, it's an unlikely defensive scenario, after all!).
I'm hardly the world's most experienced hunter - far from it! The animals I shot in Africa during the 1970's and 1980's were all taken for food, not for trophies, and I hunted only when I didn't have access to other supplies. Whenever possible, I used a rifle, because longer-ranged shooting demanded it; but I sometimes used a handgun at closer ranges, or to finish off a wounded animal. It was my experience (and that of most of my colleagues and friends at the time) that bigger, heavier handgun rounds worked a lot better, and a lot more often, than smaller, lighter ones. The .44 Special, .44 Magnum, .45 ACP, .45 Colt and .455 Webley all did pretty well. The more commonly encountered .38 Special, .357 Magnum and 9mm. Parabellum (using the bullets available in the 1970's and 1980's) did not. All too often, animals shot with the latter rounds simply ran off and were lost. They may have died later, but if we couldn't find them, we couldn't tell.
Unsurprisingly, when the same rounds were used for self-defense against human opponents, the same results were encountered. Bigger rounds usually (albeit not always) did better than smaller ones, and produced faster, more effective results.
I accept that today, bullet technology has improved to the point that smaller rounds are more trustworthy than their less sophisticated predecessors. That's why I'm willing to carry a high-capacity 9mm. pistol when round count is likely to be an important factor. Nevertheless, that same technology has improved for bigger rounds as well as smaller ones. What's more, if that technology is defeated by "street conditions" (e.g. a hollowpoint cavity is plugged by material from a thick, bulky outer jacket, so that it no longer expands in flesh), smaller rounds will be less effective. Bigger rounds, on the other hand, don't get smaller if they're plugged! They still make a larger hole.
In a situation where I have limited ammo capacity (for example, in a smaller pocket pistol or revolver, or in a state that mandates magazine capacity limits), I'm going to carry the biggest, most effective rounds I can, because I've learned the hard way that they generally work better than smaller ones. If I have a choice between a 5-shot snub-nose revolver in .38 Special or .44 Special, and my pocket is big enough to accommodate either, guess which I'll carry? And if I can carry a Springfield XD-S with either 8 rounds of 9mm. or 6 rounds of .45 ACP, I'm sure you can figure out my preference.
No handgun round can come close to the effectiveness of a good rifle or shotgun round - that's a given. (We discussed this with reference to projectile weight and energy levels in a previous article.) Nevertheless, I want the best possible defensive performance I can get, subject to all other limitations that may apply. That's why I took Mike's advice to heart. It squares with what I learned the hard way over many years in Africa, as discussed above, and it squares with what I've heard from a number of experienced US hunters and shooters. Therefore, I take his advice seriously.