I know regular ammo (i.e., metallic cartridges) will last almost indefinitely if properly stored. How about shotgun ammo?

Paper or plastic?

Edit: Sorry, I couldn’t resist. A few years ago, I shot up several cases of Winchester Super X labeled, “All New Plastic”. I’ve also shot paper shells that predate 1962. As with any ammo, I’m sure it depends on the way it was stored. If the boxes are clean and the shell cases aren’t split or bulged, it’s probably fine.
The best way to tell if it’s good is to shoot some.

__________________
"I also cook."

Last summer I shot some paper cased 16 gauge shells at my stepfathers place in Oregon. No problems, I think these shells where over 40 years old.

I have some really old ammo (WWll era .45acp .38 special, .32acp, .380 acp, shot shells) and have had no problems with it what so ever. In fact, the only ammo I have ever seen degrade to unusable status would be .22 long rifle rounds. After a while, they seem to develop a while film that will not allow them to chamber. My Dad who recently passed away, had several bricks that are not much more than paper weights now. They will not chamber into a revolver at all, and I have been hesitant to try them in an auto loader for fear that they will get stuck in the chamber. Other than that, if they look OK, they will more than likely shoot OK.

Chief38

You know, I thought about specifying plastic, but thought, aw, nobody will, ask. I should have known better. As far as shooting to find out, it's not ammo I have, it's ammo I'm thinking about buying, i.e., stocking up if I find it cheap enough. I don't want to lay in a ten year supply and have it go bad in three years.

Half a century or longer is more like it.