Ammo - a renewable resource?

Well, not exactly. But there are things that can be done now to make sure that you have enough ammo when you need it.

If you have brass-cased, boxer primed ammo it can be reloaded. You will need reloading equipment, plus bullets, powder, and primers. All that sounds expensive, but it isn't when compared to the cost of ammo these days. A renewable source of bullets *is* available if you have bullet molds for the calibers you use. Lead can be scrounged or salvaged. The best is "hard cast" which is an alloy of lead and tin (usually), but in an emergency pure lead can be used if the bullets have the correct diameter and you don't try to push them too fast. Although it's theoretically possible to load some calibers with black powder, and black powder can theoretically be made, I wouldn't try it or depend on it. Better to simply stock up on the correct gun powder while you can.

Regarding "boxer primed", be aware that some European or Russian ammo may be Berdan primed, even if it is brass cased. And if so there is no easy practical way to reload it. Boxer primed ammo has one hole in the center of the brass when the bullet is pulled, the powder removed, and you look at the bottom of the inside of the case. Berdan primed brass will have 2 little holes instead of one in the center. Also, the Berdan primers that I've seen so far look rounded when looked at from the outside of the case, while Boxer primers look flat. Best to buy some brass cased boxer primed ammo now, or at least some "once-fired" reloadable brass and primers. Widener's and other places sometimes have some good deals on bulk once-fired brass and bulk new or pulled bullets in the military calibers.

.22 ammo is cheap compared to other calibers and it is wise to have a good supply. Shotshells are outrageously expensive, and I don't know if there is a way around that. I know that they can be reloaded, though I've never done it. But that would require another set of reloading tools. And components are not as cheap or easily obtained as they used to be.