Whoever told you this was probably trying to sell more ammunition; modern ammunition is good for decades at least. In the present, use of old ammunition (a few decades or more) is discouraged because the old formulations of primer compound produce corrosive hygroscopic metal salts that will rust your gun badly if you're not dilligent with cleaning. Very cheap old surplus ammunition from overseas is something to be wary of, but that's mostly because of bad QC that made that ammunition unreliable or dangerous from the day it was made.
As for atal or sling, unless you've been practicing with these since you were a child, I think you'll sooner starve to death than score yourself a single meal. The cultures which used those tools had people practicing with them for years before they were useful with them. A sling is easy to make, I encourage you to try it out. I used a pair of shoelaces I bought at the grocery store for $2. It is not easy to even get the projectile flying in the general direction you intended, so if you try this make sure you're far from any buildings or bystanders...
(But really, I recommend buying some canned food. It is unlikely any infrastructure collapse would last more than a few weeks. Any scenario where you have to hunt for food at all, let alone for years, seems exceedingly unlikely.)
I doubt that people are stockpiling ammo for a short term disruption. The point at which tens of thousands of rounds becomes useful isn’t a few weeks disruption in food distribution.
To justify my stance, in a long term survival situation slings are for low risk low reward hunting. With even moderate practice they become very high calories per resources and time invested while your doing something else. Aka, if you’re collecting firewood and see a squirrel, vs specifically looking for squirrels. That’s still true if you’re missing 95% of the time.
Plenty of active bow hunters are around to tell you how long that takes to learn. Unfortunately, manufacturing arrows and replacement bows takes significant effort. Atal are generally worse than bows, but vastly easier to manufacture and maintain.
As to ammo it’s very much possible to find good ammo that’s 50 years old. Depending on specific ammo to still be good in 50 years is a very different thing when you can’t depend on climate control. That’s not a concern at 70+ but a 25 year old presumably has a longer time horizon.
People stockpiling guns may have fantasies about a thousand years of anarchy after an apocalyptic 'SHTF', but their belief that this is likely doesn't actually make it likely.
I completely agree. However, the accuracy of their predictions is independent of how their preparing for that risk. It’s often said to prepare food and water etc for short term disruptions, but having sufficient water is vastly more important than having sufficient food.
As for atal or sling, unless you've been practicing with these since you were a child, I think you'll sooner starve to death than score yourself a single meal. The cultures which used those tools had people practicing with them for years before they were useful with them. A sling is easy to make, I encourage you to try it out. I used a pair of shoelaces I bought at the grocery store for $2. It is not easy to even get the projectile flying in the general direction you intended, so if you try this make sure you're far from any buildings or bystanders...
(But really, I recommend buying some canned food. It is unlikely any infrastructure collapse would last more than a few weeks. Any scenario where you have to hunt for food at all, let alone for years, seems exceedingly unlikely.)