Black powder, when kept dry, does not lose its potency. i sometimes inert Civil War explosive ordnance for collectors and museums: It's done remotely in an isolated area.
A medically retired EOD friend has the distinction of being the last USMC casualty of the Civil War. He was seriously injured while inerting a Parrot projectile in about 1988.
The black powder in this round had not lost its potency when it detonated and killed the guy who was inerting it:
http://forums.gunboards.com/showthre...ball-explosion
But in February, White's hobby cost him his life: A cannonball he was restoring exploded, killing him in his driveway.
More than 140 years after Lee surrendered to Grant, the cannonball was still powerful enough to send a chunk of shrapnel through the front porch of a house a quarter-mile from White's home in this leafy Richmond suburb.