My post the other day asking people to describe what makes a handgun caliber effective without describing or naming a particular round was meant for more than hornets’ nest stirring or blatant link whoring (that was just a happy side effect). It was an attempt to illustrate that the definition of what makes a handgun cartridge effective for self defense covers a wide swath of calibers. The interesting thing is that the definition of ‘effective’ changes per person, and often per situation per person.
Most of the comments seemed to center around the following
First and foremost, none of the qualities of your ammunition matters if the gun you use to shoot it is an unreliable piece of shit or you don’t practice with it enough to able to hit your target. If your firearm is a quality one, then you simply need to choose the caliber that suits your needs the best. Pretending your heater has magical ‘one shot stop’ capabilities is not a good plan for self defense.
With a good firearm, pretty much anything from 9mm to .45 ACP is going to work just fine for the vast majority of situations. With the 9mm, you’ll gain some capacity, but lose penetration / power. With the .45 ACP, you’ll gain plenty of punch, but lose a bit of capacity. 10mm? Expensive to shoot, brutish recoil, plenty of power, and capacity can also be had if you’re ok with a grip the size of a brick. .357 Sig and 40 S&W can often be used in the same pistol with just a barrel change and a second mortgage to purchase the .357 ammo. .357 Magnum is a very effective round, but generally only comes in revolvers so your capacity is limited.
Regardless, you can’t go wrong with any of them. Heck, even the .380 can be effective if somewhat suboptimal.
I carry the 10mm because I enjoy the round. The increased firearm size and recoil are not major concerns for me as my frame mitigates that. I also reload my own ammo, so cost isn’t as big an issue. But, jokes aside, the 10mm isn’t perfect and is impractical for many people.
I’m not concerned about ‘scroungability’. If the SHTF and I’m forced to look for loose ammo, I’m going to take whatever I can find for whatever guns I can find as well.
Capacity is important to me because I’m not that good of a shot and I’d prefer to be able to have more rounds on hand in a single magazine than having to worry about shooting and reloading, but even then, that’s a bit silly as the chances of me getting in a real gun fight with multiple targets and mag changes are right up there with me hitting the lottery after getting struck by lighting twice while standing in the same place.
If you live in an area where your garden variety thug is wearing enough armor to stop several .338 Lapuas, you don't need a gun, you need a real estate agent.
So, relax about your ammo choice. It’s not better than everyone else’s, it’s not worse than theirs either. It has drawbacks and advantages and chances are you’ll never be in a situation where you’re going to find out what they are. Simply practice with your gun as much as possible and be situationally aware so that you don’t have to use it.