[GonzoGOP]

I've used ammo over a half-century old that has worked as well as new-manufacture.

I guess I should have added the caveat that it depends on how it is stored. Temperature changes and moisture are obviously the enemies, not really time.

[DuncanWaring]

Temperature changes and moisture ...

That would be the "conventional wisdom".

However, someone posted a tale here a little while back about finding 60-or-so linked rounds of .30-06 ammo in the California desert in the 1970s, in the area of one of George Patton's training grounds.

That suggested it had been out there baking in the Sonora/Mojave desert sun for thirty-or-so years.

He said that after cleaning it up, it shot just fine.

Hard to tell what the real rules are.

Except for "stay the heck away from that 1960s POF MkVII stuff".