The U.S. Department of Defense is being criticized by government researchers for not properly tracking ammo and as a result of that is now being forced to discard $1.2 billion worth of elderly ammunition that has become unreliable. That’s not a lot when you consider that the American military has stocks of ammo worth over $50 billion. But the criticism is accurate in that there is no one, unified, ammo tracking system for all services. That would eliminate situations where one service orders more of some type of common ammo (.50 caliber/12.7mm machine-gun rounds) while another service has a surplus of the stuff that will hit its “use by” date in a few years and should be used real soon. There is no centralized ammo tracking system because all the services resist such unified tracking systems. Each service insists it has special needs and this makes designing unified systems politically and technically difficult to pull off.
Meanwhile the Department of Defense spends over $30 million a year getting rid of elderly munitions. The shelf life of most munitions varies from 5-20 years, depending on the component (shell, fuze, electronics, batteries or propellant.) There's a lot of ammo out there that is about to hit its expiration date. When that happens, you can either refurbish the munition (preferable with expensive missiles), disassemble and recycle it, or keep it and play the percentages. This last option is not available to the United States.
To prevent these problems, most countries try to use up munitions before they reach their expiration date. This is not always possible. Using the older stuff is only possible up to a point because it costs more money to use it. Firing all the old artillery ammo in stock will wear out the artillery (the barrels are worn each time a shell is fired). Aircraft are expensive to fly, as they must be to use live missiles and bombs.. So there is always a lot of old stuff to be disposed of. And the military now has one more incentive to make their ammo using more expensive, highly insensitive munitions.
Major nations must maintain millions of tons of munitions as War Reserve Stocks, to provide a 30-60 day supply of ammo for the opening stages of a major war. It would take over a month for fresh supplies to begin arriving from factories. Replacing elderly weapons from the War Reserve leaves you with a constant supply of old stuff that has to be used or disposed of. Not too long ago, the old munitions would be dumped at sea, usually in very deep water. But that is not considered ecologically correct these days. Thus the expense of taking apart and recycling the components is often the cheapest way to deal with the problem.
The Department of Defense spends far more on refurbishing old munitions, usually missiles. Billions are spent to upgrade ballistic missiles and anti-aircraft missiles (both air-to-air and ground to air.) Torpedoes, which have been around for over a century, have long been given this kind of attention. Artillery shells, and large caliber machine-gun (20mm and up) ammo are usually taken apart and recycled. That's because the propellant (which is actually a slow burning explosive), detonators (to get the bang going) and high speed (or "high explosives") explosives are chemicals that degrade over time. The degradation makes the explosives less powerful and/or unstable. This makes the munitions less effective, and more dangerous to their users.