Slamfire--So if powder is stored in the original container and kept below 72 degrees F is autoignition a risk? I have some Blue Dot and 4350 that is coming on 10 years old. Also a couple of cans of old H4895 that may be pushing 30 years old, and were probably kept in a garage for 10 years (I inherited the stuff). It looks just like new (just checked) and smells weakly of solvent. I have shot some of the rounds that were loaded back when with the 4895 and they work just fine.
I suppose a loader should routinely check all of the powder on the shelf and make sure nothing is amiss. Hate like heck to burn the house down with a $20 can of powder for being a tight a** and keeping it rather than throw it on the lawn.
This is not an easy question to answer. Literally millions are spent every year by militaries to determine if their stockpiles of smokeless propellants are good. These guys have conventions where they exchange information. There are all sorts of propellant tests. If you want to see all the different tests the military has, look at Mils Std 286 Propellants, Solid: Sampling, Examination and Testing to be found at https://assist.daps.dla.mil/quicksearch/
If you look at this UN document,
IATG 07.20 Surveillance and in-service proof
Section 7.3 “ Climatic impact on the degradation of explosives” has an interesting table 1, for how long munitions should last if exposed to heat. Should does not mean "will".
When I have read and heard from insensitive munitions experts, it seems the risk of auto ignition increases with powder bulk. There is a theory that smaller ammunition (five inch shell or less) won’t auto combust in the case because the mass of metal will conduct heat rapidly enough to keep temperatures below auto ignition temps. One IM expert I know said that this is bogus, but you will see terms like “5 inch rule” in the insensitive munitions literature.
Both SAAMI and Alliant tell you to look for the gross signs of powder deterioration:
Home owners don’t own sophisticated test labs which conduct tests for chemical analysis and percentage of stabilizer in the powder. All you can do is look for gross indications that your powder has gone bad.
I recommend opening the tins/cans on occasion. The idea that powder in a sealed container won't go bad is bogus. Look and sniff. I recommend keeping powder in the original containers, I think smaller is better. Anyone pouring all their powder into five gallon drums is asking for trouble.