I shot off over 20 pounds of it, using 3031 specs, exactly as the books printed them with very good results.
The last 7 pounds I had, all in 1 pound paper containers with metal tops and bottoms, all went bad. They went bad after about 15 years of storage, under very good conditions. The powder started to clump and sweat. When I noticed there was trouble, the steel racks the powder was stored on, was raining rusty dust.
Just understand, this happened very quickly. It also happened inside cartridges I had already loaded. I ruined the barrel on a M70 FWT in 257Rob because I didn't clean the highly corrosive residue that was in the bore after a nasty weather shoot. I left it for a week, while I went on vacation and when I came back, the bore looke like someone had used a ballpeen hammer on it.
If your can of powder is showing rust inside, dump it in the garden. Makes great fertilizer in the flower beds.
I do know some fellows that bought that stuff in the late 70s and are still using it. Seems like it was only one batch of it that went bad. I guess I was lucky enough to get some of that batch.