300 degrees F will ignite gunpowder. Part of my job encompasses fire origin and cause cases, one of which happens to be a gun powder explosion case that occured as a result of an individual placing a gun powder container to close to a lightbulb. Radiant heat in the range of 250-350 can ignite gun powder through its plastic container depending upon the containers proximity to the heat source.Metal containers conduct heat more-so than plastic so you need to be aware of that as well. Keep the powder in the coolest, driest place you can find.