The shelf life of modern smokeless propellant is virtually indefinite, given proper conditions. Improperly stored, however, powder deterioration will occur. If you suspect that powder has been improperly stored, it should be checked for the following signs: 1) An irritating acidic odor, not to be confused with the ether odor common to most forms of smokeless powder. 2) A reddish dust, or a “clumped” appearance. 3) An oily or sticky substance in the powder. If the powder in question appears to have deteriorated, it should be destroyed at once.
It is recommended that it be burned out in the open in small (not exceeding one pound) amounts. The powder should be spread out so that it is no more than one inch deep at any point, and provides an ignition train allowing it to be ignited from a safe distance.
My personal experience with old powder is as follows; I wanted to load some .45 ACP rounds several years ago and had run out of Bullseye. I went rummaging through my secondary powder bunker and found a can of Bullseye that had to be at least forty years old; the reason I am fairly sure of its age was the sales label on the can was from a business that I know had closed its doors in the early sixties, also the can was definitely from that era. I carefully inspected the powder and did not discover any signs of deterioration so proceeded to load up a hundred rounds. Several days later I went to the range and shot the entire box of one hundred without any signs of problems, the point of aim was on the mark and the gun functioned perfectly.
Hope this helps answer your question.
