Twenty plus years ago I was using pure Potassium Nitrate (Saltpeter), it was easy to get, any major pharmacy had it, you could also get it from a Vet, or order it from a scientific supply house. Think I had my pharmacy back then order me 5 lbs. of it.
Im not sure whats in Brownells stuff, I imagine something to make it useless for black power manufacture (Charcoal, Sulfur and Saltpeter)

lead might be a PITA, trying to remove it.