Powder starts deteriorating the day it is made, but the stabilizers added to it keep that from happening at a significantly fast rate. Also, the colder it is, the longer it takes to deteriorate. So what really matters is whether or not any stabilizer is still left, and that depends on its storage history. If it passes the smell test and you don't see any red dust left behind when you pour some onto a white sheet of paper and funnel it back into the can, you are pretty sure to be good to go…for now. I just wouldn't load cartridges with it that I didn't intend to shoot in the next few months. That's because you can't tell if it is going bad in the cartridge case after it has been sealed in. The good news is that the bulk supply is likely to go bad sooner than the powder divided into individual cartridges. This is due to the random nature of how it starts and snowballs from there. The odds are just larger of it starting somewhere in a bigger quantity.
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