I have powder from the very early 70s that is good. Kept cool, shoots great.
Some powder keeps better than others. Back in the 70s I remember reading an article in one of the "digests" the title was "4895 A Quarter Century later" (or something close to that)
At the end of WWII, the author bought 100lbs of 4895 surplus. 4 25lb kegs. He used up three of them in the next few years, but didn't open the last one, and life got in his way. 25 years later, he "discovered" the las keg, stored all this time in his family's Pennsylvania barn. So, he broke it open and began testing. The powder had not deteriorated in any physically noticeable way, the only change was equal weights delivered 50-75fps less velocity than current powder off the shelf.
A ball powder 40 years old is suspect in any event. The military will only stockpile it 25 years. The Navy demonstrated it can age such that the deterrent coatings are deteriorated faster than the rest of the powder, giving it a faster burn rate.
I was unaware of the military shelf life of ball powder, but it does make sense. I suppose the Navy keeps a pretty good eye on this kind of thing today, not wanting to repeat past embarrassment. When we got into WWII, the Navy was apparently surprised that the gunpowder reserve for their battleship guns, which had been stored in barges on the Potomac for 20+ years wasn't quite the same as when they put it in storage.
But, in this case, the issue isn't if the powder is still good, the issue is WHAT IS IT???
and there's no way to know, for certain.
When you are working with a material where "not quite enough", "just right", "hmm a little too much", and "KA BOOM!!!
" will all fit in the same case, not knowing or even having a reasonable idea what you are dealing with is dangerous.