How long are bullets "safe" before becoming unstable or the shell is corroded? How do dispose of "bad" ones?

Ammunition can be good for a very long time if you store it properly. Like in a cool dry place. I have fired 50 year old ammo that was just fine. I also have some reloads that are over 20 years old that work just fine to. If you have some ammo that you want to dispose of you can pull the bullets using a bullet puller. Then you can soak the powder in water or even burn it if you want. Just be care full. Then that leaves you with the unused primer in the brass cartridge. You can soak the cartridge in water and that should ruin the primer enough to keep it from functioning.

Safe Bullets

Bullets are safe for at least 10 years someone told me once. You take the gunpowder out of the shell and then soak the powder in water for 2 days and then put it in a plastic baggy and trough it out.