I trust that you guys know better than I, but I also heard that the newer ammo does degrade. Hoping it's just a conspiracy myth, but was there legislation to require the addition of something to the ammo in the last 20 years or so that would cause it to degrade? I wouldn't want to stockpile too heavily were that true. So just looking for some assurance.
The older, "corrosive" primers lasted longer than the newer ones do.
I've not heard anything about a "degrading agent" being added, there was talk of mandatory "taggants", specific chemicals added to powders that could track the product from production to final firing point, but this hasn't been done, yet.
Here's a good "primer" on ammo storage:
http://www.frfrogspad.com/miscelle.htm
Q. How long will ammunition last in storage?
A. Properly stored ammunition can last at least 40 years or more without any problems. However, the caveat here is "proper storage."
The method the military and ammunition industry use for long-term storage of ammunition is very old and very simple. Make a concrete bunker with walls about a foot thick. Then cover the whole thing about a yard deep with dirt. This construction is called an "igloo". The igloo produces a remarkably constancy in temperature and humidity inside, requiring neither power nor adjustment. Using this technique, modern small arms ammo may be stored for 40 or more years with no material degradation. Conversely, ammo "stored" in a hot car trunk may be dead as a mackerel, or wildly inconsistent in a single summer. However, not all of us have an "igloo" handy. Given even moderately consistent conditions most modern ammunition components are fairly resistant to degradation in the short run, say 10-15 years, absent high temperatures and/or constant temperature fluctuations.
To hit the high points of home storage very generally
1. In general, it is the PRIMER that you are worried about. Absent excessive high temperature and/or humidity, modern smokeless powder is very resistant to degradation in storage. As an interesting aside, corrosive priming compounds that use to be commonly in use have longer storage lives and are more resistant to degradation than comparable non-corrosive priming compounds.
2. No matter where you store ensure there is "dunnage" (i.e. 2x4 wood) under and between each layer stacked. Also ensure there is air space between stacked cases on the same layer. These provide air circulation which is crucial.
3. Humidity--Drier is better, but in sealed cans will make little difference if dunnage and air space are maintained. The ammunition should be packed with a desiccant. You can purchase a commercial product or go the "do-it-yourself" route. Go to any construction site and ask the straw boss if there are are any broken sheet rock boards around or some wallboard scraps. There will usually be. Sheet rock is gypsum and hydroscopic. Get a few pieces and cut them to about the size of a deck of cards square. Cook them in the oven at about 200 degrees for a few hours to drive the moisture out of them, then put one in each of your ammo cans. The piece will absorb what little moisture there may be in your ammo can can giving you a nice dry environment.
4. Temperature--This is a big one with lots of details. Good ammo is like good wine. Both like a constant, even temperature around 65 degrees F. The constancy of temperature is more important than the temperature itself. (This is a dandy excuse to build a wine cellar to store both.), And, as a wise man once said, "you can never have too much of either."
For short-term storage of general-usage ammunition, the most important factor is to keep the ammo out of excessive heat--say over 85 degrees. Excessive heat degrades ammunition. Ammo stored in car trunks is the most common victim here. Low temperatures do not harm ammunition per se. What degradation may occur is caused more by repeated temperature fluctuation than by the cold. (As an aside, double base powders can perform erratically when USED in very cold temperatures, but this is not a function of storage.)
At this point we probably should explain what we mean by "degradation" If you're storing MG ammo or "rattle battle" ammo, for a few years, the garage should suffice nicely, given the constraints above. The standard deviation of the velocity may go up slightly, but I suspect you will not notice a thing. On the other hand, if you are storing match ammunition, I'd recommend keeping the stuff in a place with a more even temperature. The bedroom closet, where the temperature stays nice all year, for instance. With something as precise as match ammunition even a little degradation could be of consequence.
Invest in a "min/max" thermometer that shows both the minimum and maximum temperature recorded. They run 10 bucks or so. Check your storage area monthly for signs of excessive temperature (check the min/max) or other degradation (rust on cans, etc.). There are no magic procedures. Just remember that equipment respected is equipment that will be reliable.
{As an example of what is possible, some years ago I fired some 60+ year old GI .45ACP ammo (FA 18 headstamp) that had been found in a military storage bunker. Of 40 rounds fired every one went off and 5 rounds over a chronograph averaged 788 f/s. -- FF}
Thanks to John Nichols for supplying this information--courtesy his stint with Uncle Sam.
To sum up.
Store ammunition and components in a temperature stable area (ideally 60 +/- 10 deg F)
Store in GI ammunition cans of good quality with good seals with a desiccant pack included
Have plenty of ventilation around the stored ammo cans and keep them off of floors.
If dampness my be present you can coat the ammo cans with liquid Alox to prevent long term rusting
