It is interesting how peoples views on Black powder differ. I have shot m/l shotguns for years and have always used Black powder. It is classed as a low explosive and is relatively easy to set of. I have heard other shooters saying there is no real pressure in it but i an sure very high pressures can be had!
Providing basic safety procedures & respect for it are observed it is perfectly safe. For example i personally would never load from a powder flask directly into the barrel rather always into a measure first.
Many years ago i had an accident and set of 1 ld of the stuff with an angle grinder at a range of 5ft, it was very very hot and i lost most of my hair, moustache & sideburns in the flash. That powder was at least 50 years old & caked solid but boy did it go! But for my goggles i would now be sporting a white stick. Funnily enough i never heard the bang though witnesses said it was very loud. The worst thing was i had my full membership interview at my local wildfowling club that very night and as i answered the questions bits of burnt hair kept falling on the table, i did get some strange looks but passed