Does anyone know how much black powder and regular gunpowder can legally be stored by an FFL holder? Thanks in advance

Black powder for personal use in blackpowder rifles and such, is a max of 50 pounds according to federal law - state may be different

Black powder for sale in any amount requires a BATF approved magazine - state law may be different.  A type 4 indoor moveable with a maximum of 50 pounds is what works for most gun dealers.

Mark

i think if you have alot, store it undergroud like the military does. the burial tubes work real well. also put in a desiccite pack. it will last longer, stay the same temp pretty much year round, your family will be safe, and if you do have a fire, they will ask you if you have gun powder inside. then they will let your house burn down while ATF is on the way. you will also make the evening news as a right wing nut!