I've become interested in the WROL (Without Rule Of Law) and SHTF (S%!t Hits The Fan) topics, and there's quite a bit on the internet. For those that don't know, someone who takes an active and serious role in preparing for such catastrophes -- be it man made or natural disaster -- are called "preppers." I'm learning that a prepper has taken things a bit further than someone who is a survivalist. I'm not sure, but I think the term "prepper" is fairly new. It's a pretty interesting world, and I've been watching a lot of Youtube videos on the topic. I've always been someone who mentally prepares for something like that happening, and I know I have most of the gear/food stores/ammo to survive, but a prepper takes it a step further and actually stages the gear for easy/quick access.
One of the topics, and the topic that I want to touch on, is the choice in firearms to choose as your WROL/SHTF weapon. Of course, you have the guys who are all about the AK, and "It's the best weapon ever because you can do anything to it, and it will work, and the 7.62x39 Soviet round is the best as a man stopper" And those that have the big revolvers in .357 because that's the most reliable handgun, in a great caliber. And of course you see a lot of guys who choose 1911s, and Glocks in .40 S&W.
I agree that the AK is the best choice if you're looking for something indestructible, and the revolver is the most reliable choice. And I'm certainly not going to argue the effectiveness of any of the above mentioned rounds. HOWEVER (draws long breath), I am going to argue that those choices are a bit misguided. In my humble opinion, you shouldn't choose your weapon by brand or model, but by caliber. Of course, if you don't own a lot of guns, you have no choice to use what you have. But, if you do have a choice, your order of importance in picking out a weapon should be, 1. caliber, 2. reliability/durability.
In choosing calibers, there's really only a few choices. In handguns, the number one choice is 9mm. In rifles, .223/5.56. If you want a high powered rifle, .308/7.62. You could argue until your blue in the face about the effectiveness of these caliber choices, but it doesn't matter. Is the 9mm the most effective pistol round? No. Is the .223/5.56 the most effective rifle round? No. But I will tell you this: a handgun that you have in 9mm, with ammo, is more effective than a .40 S&W Glock without ammo. And no matter how many thousands of rounds you can store up before WROL/SHTF, depending on the circumstances, you do not know how long WROL/SHTF will last, and you will eventually run out of ammo, or become permanently separated from your ammo. So you will have to scavenge. And since 9mm and 5.56 are our military standards, as well as the standards of the entire Western world, you will always be able to find those rounds. If you lived in Russia, the 7.62x39 would be the best choice, but you don't, so it's not.
Sure, the chances of WROL/SHTF lasting more than a few weeks, or months is low -- like New Orleans after Katrina, but if you're a prepper, you need to prare for WCS (Worst-Case Scenario). I would say, probably worst case scenario is Somalia. A complete and utter collapse of government -- a true anarchy. Or perhaps Rwanda-type situations are even worse, when there is genocide. My point is that in those situations, especially Somalia, there has been WROL for over a decade. Even if you had 10,000 rounds, in that amount of time, you would have either ran out, or perhaps been separated from your ammo. So, you definitely need a caliber that you can readily scrounge up. And the 9mm and 5.56 you'll be able to find on or near any military base. You'll also find it on bodies of military personal that you stumble upon, or even in abandoned military vehicles.
For handguns, I would say seconds are the .40 S&W, and the .45 ACP. A majority of law enforcement agencies/departments use the .40, some use the .45 (and also the .45 was our previous military standard -- and it's the most popular handgun cartridge in our country -- so there's a lot of that around.)
In sum, while there are better choices for self-defense, there is no better choice for availability. As the saying goes, Amateurs talk strategy, professionals talk logistics. And in talking about WROL/SHTF that could potentially last for an extended period of time, resupply will be crucial.