I agree with Cooner. I have not shot 200 year old powder, but we came across some that was at least 60 years old, and it fired just fine. The key is to store it somewhere dry. If moisture does get into Black Powder, all you have to do is take the cap off the can, and put the can on a warm surface, like a stove top, in a safe place away from open flame. When the can heats up the moisture will be evaporated out of the can. I would not heat the can any hotter than I could comfortably hold the can in my bare hand, however, for safety sakes. Its would not be necessary to dry the powder. Probably no more than 10 minutes on the stove top, with the oven on at a low setting, or set out in the sunlight on a cement patio, or stairs, or even on the hood of your car, would get the powder dried. If it clumps a little, just gently shake the powder in the can and it will break up the clumps. Powder is run through a process that coats the grains with graphite, to reduce the change of static electricity ignition. Generally when moisture gets into powder, its the graphite that is sticking together, and not the actually powder. If you have a clump that will not break apart from gentle shaking, its probaly safest to throw away the clump. pour water on it, and when you have made a black tea, our it on your garden. The nitrates are good for the soil, as is the sulfur. The carbon will break down in the ground, easily, over time, and be used by the plants to make new cells.