cool dark place,,,virtually forever. There's alot of stuff from the Spanish American war and WWI era thats still perfectly usable (although most of it has probably been stored in less than ideal circumstances by now).
I have fired some reloads I made back in the late 60s and early 70s. They performed as good as when they were made. They were stored mostly in a cool dry area, but nothing special. Had a bunch of old RXP reloads made in the 70s and they broke targets like they did back then. Not one dud or blooper in almost 1000 rounds of ammo.
I gave some fed. papers loaded light for a brother who showed some interest in about 1976. When he died in 2008, I got the chore to clean out a lot of shootin' stuff and sell some guns for the widow. There was no thought of selling the old shells but recognized the stuff I had cobbled together 32 years earlier. I took the shells to the club and shot box after box over 3 weeks and never had a bad shell and they all looked like I'd loaded them the day before. They broke a lot of targets too. My brother had moved this stuff from San Jose, Concord, and Ukiah in California over the years, retired from his vineyard early in the 2000s, was in New Mexico for 3 years, and ended up in Sequim, WA. This covered many different weather and various storage situations over the years. They were Fed. papers, Fed. primers, 700X powder under CB (I think) wads. I wouldn't worry too much about shelf life unless you just do something really dumb....breakemall.....Bob Dodd