1. Modern gnpowder burns slowly if set on fire with a match and not enclosed in a breech. The higher the pressure in the breech, the faster it burns and releases gas.
At atmosperic pressure it burns rather slowly.
A bullet that cooks off in a fire will travel about ten feet and bouce off of you skin. The amount of pressure required to remove a bullet from a cartidge case is about 60 lbs.
Age seems to have little effect on ammo.
Any problems with age and how ammo is stored will result in a failure to fire rather than a bigger explosion.
Blackpowder is not effected by by age whatsoever. 200 or 300 year old black powder is as manufactured. There are a number of cases in which very old black powder was tested and it was found to be the same as the day it was manufactured.
If black powder is wet it can be dried out and used without any problems.
A number of companies have tried to develop electrically fired black powder guns and static electricity is not sufficient to set it off because black powder is electrically conductive and it absorbs the charge like a sponge. I have seen test results with 40,000 volts (it will burn you) of static electricity and the results are nothing. Nada.
The problem with dynamite is only with very old dynamite, 1900 or so. The newer stuff is quite stable.
TNT and mercury fulminate probably aren’t so stable with age.
I made some electrically fired muzzle-loaders 30 years ago.
So why don’t they add steel wool shavings as a booster? It seems that bridge the gap.