Don't be tempted to use powder of unknown origin or that which has been loaded into a dissimilar cartridge, mortar shell, or what have you. For example, you could experience disaster if you tried to load rifle cartridges with powder scavenged from pistol rounds. Regardless of the source, proper storage of powder is essential if it is to last. Because the solvents left in many powders are necessary to preserve their power, it's important to keep them in scaled metal containers. Don't place powder in glass containers; light quickly damages powder . Heat is another enemy of powder because it dries the moisture in the powder quickly and causes it to deteriorate. Once this process occurs, the powder ages quickly, undergoing chemical changes that will eventually ruin it. Storing powder in an attic or a hot toolshed will make it unsuitable for use in a short time. Cold storage of powders can be ideal; however, a constant temperature is better than one that dips to very low temperatures and then climbs to more moderate ones . If proper storage is used, you can expect powder to last for 20 years or, if kept in a refrigerated area at a constant temperature, up to 50 years. Rust-colored dust on the surface of some powders indicates that they are deteriorating. Other bad signs are corrosion on metal parts of containers and the replacement of the ether/alcohol smell of the powder by an ammonia odor. When any of these signs are found, the powder should be discarded. If the old powder is in cartridges, the brass and bullets can be salvaged, provided the acid by-products of corrosion haven't actually attacked the brass and copper. Chances are that the primers will be unusable if the powder is bad, but you might want to test the primers to see if they can be salvaged. If the primers are still good, they can usually be popped out with a depriming tool or the resizing/depriming punch on a reloading press (the only exception to this rule is military brass with crimped primers) . When removing live primers, care should be taken to operate well away from powder, other primers, or flammable materials. And, of course, it is important to wear eye protection as in other reloading operations. Don't be tempted to use powder to load cartridges once it has deteriorated. In addition to not firing consistently, it may create a "squib" firing that lodges a bullet in the barrel. With a semi-auto or selective-fire gun, this contributes to inadvertently sending another shot down the barrel and blowing up the weapon. You're better off not risking this. If you manufacture your own powder by following the steps below, remember that some types of powder that deteriorate may also generate enough heat to create spontaneous combustion. For this reason, you should store the powder in an area away from your house, check it from time to time, and dispose of any that is no longer good by scattering it over the ground in an open area where it can decompose (and act as a good fertilizer in the process) . It's possible to bum old powder, but the fumes can be toxic and the process is almost guaranteed to attract unwanted attention . There are a number of powders that can be manufactured for cartridges. All are dangerous to varying degrees; the greatest room for disaster lies, however, in manufacturing modern powders. One mistake with these and you can create a serious explosion, fire, or acid spill. Making powder is extremely dangerous, even more so than making primers. You'll also face a lot of unknowns if you're making your own powder. Although small grain sizes are ideal for pistol ammunition and larger grains for larger rifle ammunition, sizing is relative and varies greatly from one cartridge to another. Too, shotgun ammunition tends to vary greatly, with slower burning powders being used for large bores and faster powders for the .410 and smaller bores. Because some powders are inherently faster burning than others, regardless of the size, figuring the best size for any given gun is tricky and requires a lot of cautious experimentation. All of this necessitates an overly cautious and conservative approach if you are to survive the process. Some of the more common propellants you might use in a firearm are black powder, ammonpulver, cordite, guncotton, and potassium nitrate mixtures. Often, combinations of these are found in commercial powders, but it is generally wise not to experiment with mixtures too much since you may create a dangerous powder in the process. Storage of do-it-yourself powders is even more of a problem than with commercial powders because most described below are hygroscopic to some extent may decompose more quickly than commercial powder, and some — especially black powder — are more akin to explosives than propellants. Care should be taken to keep your powder in a cool place and in a tightly sealed container designed to rupture if exposed to a fire (to prevent the container from becoming a bomb!) . You can't be too careful in making, storing, and using gunpowder or smokeless powders.