Most people go way overboard with ammo. Unless you're going to be doing a lot of hunting you probably won't need it, in my humble opinion.
Reality is that if you are in battles so regularly that you need to have tens of thousands of rounds squirrelled away then you probably need to think instead about getting out of that environment. I've been in gunfights all over the world and know that the reality is that the more fights you're in, the more likely you are to get shot. If you find yourself in a gunfight every time you step out the door then WTF are you sticking around for? Go someplace less hot. Sooner or later your number comes up, and it doesn't matter if you have ten rounds in the basement or ten thousand. It only takes one shot to get yourself dead, and that ain't good prepping.
Lots of people seem to think if they just squirrel away enough guns and ammo they can get through anything. I've personally witnessed the fallout of all kinds of failed societies, and while prepping for some kind of multi-decade anarchy can't hurt, the reality is that there is very little modern or historic precedent for this sort of situation. Some sort of order is always restored. The big question is what that order will look like, who will be in charge, and what the new rules will be.
In the case of the coming economic collapse, the thing to remember is that we're not going to be talking about post world war europe or japan, or north africa at the end of the cold war. The bridges and roads will be here, the power plants will not be destroyed, even if they are switched off for a while. If there is disorder it won't be forever. If things happen the way they typically do with runaway inflation and other such nonsense, you'll get civil disorder, possible government change - but someone will step in and restore order.
The only exceptions to this rule that I've observed are places like North Africa, where the infrastructure simply doesn't exist because decades of war have destroyed what little is there, and where tribal feuds run deep. And as bad as things could get here, the plain truth of the matter is that people in the US are far less tough than people over there. Few people here have ever heard a shot fired in anger. You will not see the kind of heavily armed posses here that we ran into in Somalia, and that still are at it over there.
If you get a riot on your street, probably standing on your porch with a super soaker would be enough to scare them away.
If I'm wrong, and this place does turn into Somalia somehow, why would you stay here? FInd a more stable English-speaking country and get out of here. I mean, seriously - I fought multiple combat tours in the name of this country, but if it gets that bad I'm gone. I'm not staying here and struggling to survive for decades, and I'm not raising my kids in anarchy.
As a case study - I have a very good friend who is descended of Ukrainian nobility. When the Bolsheviks came to town they rounded up the landowners (the nobility), killed them all, and seized their land for collective agriculture.
My friend's great grandfather smelled the poo on the wind and converted much of the family's wealth to diamonds and other hard, easy to carry assets.
His neigbors all thought it would be smart to hole up on their land with guns and ammo. Long story short, they're all in shallow graves somewhere in the Ukraine. Their land was seized anyway, but my friend's ancestor was able to bribe his way through all of the roadblocks and get his family out.
The spent two generations looking for a new place to settle, and it wasn't easy, but eventually they found a new home. In the unlikely event that things got that bad, I'd be gone.
My friend's great grandfather got his family to safety with one flintlock pistol, haviing never fired a shot. Now if that's not your bag and you fancy yourself to be John Rambo and think you can fight for decades without taking one, by all means, store up thousands of rounds and all, but I think that's a stupid waste of resources. If things are so bad that you need tens of thousands of bullets and you're really cocerned with survival, you should be thinking more about jumping ship than digging in.
Remember too that without access to serious, hard-core medical care, and that right away, you're dead if you take even a relatively minor hit. I've been shot three times. I survived all three times because of the speed with which I was removed from the battlefield and transported to a safe placce to get good medical care. If you don't have a medevac unit ready, and you get shot in the arm or the leg or the foot or whatever in a firefight, all the other guy has to do is wait for you to bleed out.
So much talk by preppers about about ammo and guns, and I seldom see any real thought about what the implications of needing of that are. Do you really expect to fight Hamburger Hill at your home, day after day, year after year, and survive that? Ask any real soldier and he'll tell you you're nuts. Get the hell out of that situation.
There is no hard and fast rule about this and I'm likely to take a lot of flak for my opinion, as the conventional prepping wisdom seems to be that you should stockpile and fight your way through it like Rambo. I think most of the people who think this way have probably never been in a real firefight or a real war or seen what real anarchy looks like, and are wedded to romantic ideas about defending their property and their rights and all that kind of thing. All noble thoughts and all, but I would argue that if survival is your primary objective then you should be avoiding conflict, and trying more than anything else to find a place to live where you're not going to get shot at every day.
If it's the principle of the thing (I'm going to die in my homeland, etc.) that's important to you, dig a trench. Build a wall. Buy a tank. Prepping for an Alamo-style last stand and prepping for survival are not the same.