According to Bill, if he could not get black powder, he would use T7, and his testing showed it had no perchlorates in it, even though the MSDS sheet said it did.
He said "they" used the same sheet as Pyrodex so they'd not have to go to the 'expense' of writing up another MSDS sheet.
Propellants which have perchlorates in their composition, produce VERY corrosive fouling, that is "activated" by moisture. The requisite moisture can be absorbed from the air, or merely from the water based, lubed wet patch used in loading. This is what Bill told me & all of us.