There are currently something like 55 standard handgun cartridge options between .17 HMR and .500 Smith & Wesson. Any of them could be used for self-defense. It’s just that some are better than others.
But who is to say which of these is the best? In my opinion, you can eliminate the half dozen or so at each end of the spectrum, but in doing so, you would also eliminate FN’s 5.7×28 cartridge on the small side and a bunch of wrist-breaking revolver loads on the heavy side. But you can see it’s not as easy as jumping right to the middle of the list and picking just one cartridge.
I would never suggest any of the big boomers like .500 S&W or even the .454 Casull. Even the .44 Magnum has what I would consider to be oppressive recoil for a defensive round. But .45 Colt has stopped a lot of fights over the years and still works well today.
So, aside from just reaching for the nearest 9mm and calling it good, how do you choose? (BTW, are you aware there are seven different sizes of 9mm, from 9mm Japanese Revolver to 9mmx21? The most common is the 9×19. Some people call it 9mm Luger, 9mm NATO, 9mm Parabellum or just 9mm. But, I digress.)
I will start a fight here by saying it really doesn’t matter which caliber you choose to shoot. But there are some differences you need to know about.
Ballistics is a physics problem, and with physics there is one universal truth: You can’t get something for nothing. Some English scientist said it more eloquently, mentioning something about an equal and opposite reaction. But I like my way.
With pistol rounds, you are basically poking holes. You will get some hydrostatic shock, but you are not getting a big permanent wound cavity the way you do with a rifle. Pistol bullets are just not going fast enough. So, if you want to poke bigger holes, you must use bigger bullets. Yes, you can use hollow-points that expand when they hit tissue, but when you compare apples to apples, that means if you want to poke a bigger hole you need to start with a bigger hollow-point bullet.
To move that bigger bullet, you need more power. So the guns shooting bigger bullets will have more recoil than guns shooting smaller bullets. Yes, you can offset some of that felt recoil with a heavier gun — remember you can’t get something for nothing — but a heavier gun is more difficult and uncomfortable to carry all day.
You could also choose between poking a few big holes or lots of smaller holes. Once again, say it with me, you can’t get something for nothing. So there will be a balance point where a gun with a few big bullets weighs almost the same as a gun with more of the smaller bullets.
You can see that choosing a caliber for your defensive pistol will be a series of compromises.
Here is what I suggest: Find a gun that fits in your hand comfortably and is light enough for you to carry all day. Then look for the largest caliber in which that model of firearm is offered and test-fire it. See if the gun is comfortable when you shoot it. If you don’t like the recoil, choose a smaller caliber. Then look for top-quality defensive ammunition that penetrates at least 13 inches into the human body while expanding reliably.
That should give you a good place to start. Of course there is more to consider, but right now, this information will help you get started.