This stuff isn't like milk, meat or cheese. Its metal, mostly. The seal is metal on metal, forced fit. Air can't get in and air can't get out. I'm always mystified about the dry conditions everyone suggests. What's going to go wrong? They store smokeless powder under water. Its just not water sensitive. Rimfire ammo is even more secure, its usually got a wax seal with the heal type bullet. No other place for air, etc to get in.
Someone said above it will out last the shelf. I agree with that. I buy old ammo when its cheap. Many times I've been tempted to promote the idea it went bad in a few weeks, just like milk. If only to drop the price. I've got a bunch of ammo from the 40s and 50s. I shoot some from time to time. I'm getting old now, and I've shot a bunch of it. I've never had any problem I can assign to age of ammo. Most of the 1950s 22s shoot better than today's production. I'm guessing its because of better quality control back then, and every rim got its dose of priming compound. Unlike today's production.
I've got a fair amount of Super-Vel ammo I bought back in the day. I add to it every time I see any at gun shows, at a fair price. Shoots and seems just as good as 40 years ago.
But if you've got some you don't trust, just ship it this way. If nothing else, we can pull the bullets and reuse them. The cheapest components are the primer and powder, the expensive ones are the case and bullet.
A while back the anti gun forces were promoting the idea of making ammo de-activate itself over a specific period. A few years was suggested. It was designed as an effective way to side step the Constitution. Make the ammo inert, and then tax it and restrict its use. The problem being that no one has come up with a way to do that.
So my advice is pretty simple. Don't trust anyone who suggests ammo goes bad over time. They probably have ulterior motives. Not in your best interests.
. Shotgun shells i have two military surplus steel ammo cans one for bird shot and the other for buck shot.
