When properly stored, an unopened container of smokeless powder has an indefinite shelf life, but once it is opened, the stabilizers it contains begin to slowly but surely weaken. Even then it can still last for a very long time.
During the 1960s, a hunting pal and I pooled our resources and bought a 60-pound keg of H4831 from Bruce Hodgdon. We loaded it in everything from the .220 Swift to the .300 H&H Magnum, and while velocity with the Swift was not as high as it would have been with a quicker-burning powder, accuracy was great, and at 60 cents per pound who cared about a few additional fps in bullet speed?
I still have a couple pounds of that powder, and best as I can tell it is as good as it was when I bought it more than 40 years ago. Hodgdon had purchased the powder on the military-surplus market, so one can only guess how long ago it was actually made.
Powder in loaded ammunition can also have a very long life. I am told that some of the .50 BMG used in Desert Storm had been in storage since the 1940s.
Commercially loaded ammo can have an equally long life. Until a few years back, the tables of a dealer who attended a local gun show were always piled high with beautiful vintage boxes of ammunition, some of which went back to the late 1800s. Most of it was for collectors, but he often priced cartridges in slightly damaged packaging much lower.
I bought a box of .22 Hi-Power ammunition loaded by Savage during the 1920s, and not only did every round fire in my Savage 99, it was quite accurate to boot. That ammo was probably close to 80 years old when I shot it.
Subjecting powder to unfavorable conditions can shorten its life considerably, even when its container has never been opened. Quite some time ago, a friend who had just completed a large storage building out on his farm invited me to share some its space, so among other things I stored several unopened canisters of powder there.
The building was neither heated nor air-conditioned, so inside temperature ranged from extremely hot during summer to extremely cold during winter. I actually forgot about the powder being there and did not retrieve it until about 10 years later. Two of the canisters had obviously gone bad, and while the others might have been okay, I disposed of them as well.
You can tell if a can of powder is good or bad by giving its contents a sniff test. If the smell ranges from no detectable odor to resembling alcohol, ether or acetone (from its solvent content), it is okay. If you get a terribly unpleasant, acidic odor that fries your nasal passages, extreme deterioration has taken place. The odor is difficult to describe, but my nose says the experience is quite a bit like taking a strong whiff of the fumes produced by muriatic acid.
Any change — regardless of whether it is physical, chemical or otherwise — indicates time for disposal. If a brown or rust-colored fume escapes from the container when you open it, the powder is unsuitable for use. The plastic cap on one of the containers of powder that went bad on me was originally blue in color, and the chemical changes that took place inside had actually bleached it snow white. Sudden rusting of the metal cap of a container is also a sure sign of bad things going on inside.
If you suddenly begin to experience wide shot-to-shot variations in velocity or a noticeable reduction in velocity of a favorite load, the can of powder you are using may not gone completely bad, but it will probably get there sooner than later. Although quite rare, it is possible for powder to deteriorate to the point of self-ignition — another reason for occasionally giving each opened container in your reloading room the sniff test.
It is okay to load ammo out in the garage or other non-environmentally controlled area, but powder should be stored in a cool, dry place. While recently discussing the subject with Ron Reiber, head ballistician at Hodgdon Powders, he pointed out that powder in useable condition stored properly in the home is actually safer than some of the aerosol products commonly found there.
But we are talking reasonable amounts here. Those who have stockpiled enough to supply a small army should consider other alternatives. One of my neighbors, who will probably never have to buy another primer or pound of powder for the rest of his life, uses several old refrigerators located in an insulated outbuilding.
Powder companies recommend disposing of deteriorated powder by burning in small quantities (a pound or less) in an isolated area. The pile should be spread out so it is less than inch deep and enough reserved for making a narrow ignition train reaching a safe distance away. Laying a sheet of crumpled newspaper at the end of the train and lighting it with a match gives you time to retreat even farther away before the main pile of powder starts burning.
Like fertilizers, smokeless powders contain nitrate, so thinly spreading it on the lawn is another option.
It is impossible for me to squeeze every detail about the subject into the confines of my allotted space, so I strongly urge all handloaders to do a web search for "storing smokeless powders." If you still have questions, call the technical service guys at Alliant Powder at (800) 276-9337, and while doing so ask for the free Reloader's Guide. In addition to containing the rules and regulations that apply to the storage of powder, it has about 70 pages of load data for shotguns, rifles and handguns. A similar booklet on IMR powders is available from Hodgdon at (913) 362-9455.