Preparing for armageddon isn't really sensible, because you can't prepare for it. If it comes, it comes. Being on good relations with people is going to help you out more then the 100.000 rounds stockpile, because the order of the day will be grouping up. You can actually take a look at post-apocalypse societies. Take a look at Somalia, Yemen, or any other similar third word dysfunctional country. People don't sit on, or need, ammo stockpiles there.
For the likely sort of disaster, which is a temporary disruption, a 50 round box of ammo will be sufficient. Opportunistic looters are opportunistic, they aren't going to assault an armed group head on, it goes against the idea of easy money.
When the war started in my country, lots of people were buying (generally, black market) guns of all sorts, but they'd buy a box or two of ammo and that's that; it was sufficient for the purpose of protecting themselves against opporunistic thugs which exploited the disruption in law and order during the first couple of years. I know of a number of incidents of people defending themselves, but I never heard of someone running out of ammo doing it, and most of the time it ended without any shooting at all, or with a warning shot; often nothing was reported to the authorities, too.
If something similar happened again, the thing I'm counting on isn't a big supply of ammo, but rather that every house has something, legal or not, and the relations with the neighbours are good. This means in case of a breakdown in law and order, anyone raising hell would be watched through many sights from many windows, something a lot more effective then sitting on a warehouse of ammo.
