At night or in a darkened place snap a cap on an unloaded pistol and be amazed at the the fireball around the recoil shield all just from the cap. If that flame gets around a loose or "pinched' or missing cap and see where a chain fire comes from.
NOW THIS IS IMPORTANT
Do not load directly from a flask. Pour powder from the flask into a measure or empty shell case or something and then into the chamber. One little spark and the flask becomes a hand grenade and your nickname becomes Lefty that is if you survive.
Black Gunpowder is an EXPLOSIVE. It is called Gunpowder to differentiate it from BLASTING powder, made using the same manufacturing process, same ingredients just a different finishing process for Gunpowder.
I cannot speak for substitutes other that American Pioneer Powder which also is an explosive.
be safe, have fun, but se your head. It is a real firearm not a toy.
Your friendly curmudgeon
Bunk