Let me make a comment about the lifetime of double based and single based powders. Both types are primarily nitrocellulose based. Nitrocellulose is a high energy compound deteriorating to a low energy compound the day if leaves the factory. The lifetime of the nitrocellulose molecule is based on the stability of its double bonded NO molecules. Anything ionic will break those bonds. And, as it turns out, the nitroglycerine in double based powders, attacks the nitrocellulose molecule. So the lifetime of double based powders are less than half that (all things considered) to single based. If everything is perfect, little to no acid left in the nitrocellulose, single base powders "should" last 45 years, and double based "20" years. This is sort of like predicting the lifetime of humans, lots of humans don't make it past childhood, but we all forgot those and only remember those who made it to 100.
Now something else about double based powders, the nitroglycerine is wicked to the surface by humidity. Water molecules are polar covalent, and that oxygen end pulls on nitroglycerine as water molecules land and take off from the powder grain. In time, the surface becomes nitroglycerine rich, and that changes the slope of the pressure curve, all to the bad.
Due to the better lifetime of single base, I have tried to avoid double base. But, I purchased kegs of Unique and Bullseye powder, before I knew this. So I am shooting the stuff up and watching for any funnies.