@CWO:
@Der:
It’s hard to believe that powder can still be good after 70+ years!
That’s actually part of the problem.�  If I’m not mistaken, certain types of explosives can destabilize over time and become more sensitive to shock.�  I think this is particularly the case with nitrocellulose explosives, whose nitroglycerin component apparently re-liquifies and seeps out of the solid matrix when it gets too old.�  It’s sort of an extreme example of the concept of the “best before” date that is more ordinarily applied to packaged foods and pharmaceutical products.
This is true. The picric acid used in hand grenades still during WWII reacts with the metal casing of the grenade to form picrate salt, which is highly unstable.
WWII era hand grenades are problem also in Finland because of the “Weapons Cache Case”. As the Continuation War against Soviet Union was turning bad, some of the Finnish officers decided to hide large amounts of weapons and explosives all around the country in case the Soviets would occupy Finland. Those supplies were meant to be used in guerilla warfare against the occupation. Since this never happened, some of those caches still remain untouched and are discovered from time to time during house renovations, building excavations etc. The weapons are still functional and often sold on black market, and the hand grenades pose a serious threat to anyone handling them and to those nearby.
edit: some typos
