Modern substitutes for black powder are far more efficient, for example some grains actually are perforated with channels and holes to allow better combustion.
I always thought black powder was a little less stable, but I’m not a chemist. That’s just what I sort of heard off hand.
It’s very prone to igniting from static sparks (black powder cartridge loading equip is made of different material than smokeless), even being stepped on if there’s a spill.