Pyrodex P is made, and intended to be used for Percussion rifles, ONLY. It has a much higher flash point( the temperature at which it ignites) than does Black Powder, and simply is more difficult, if not impossible to ignite using FLINTLOCK ignition. If it ignites, ignition is delays, and you have to deal with "hangfires".
To get adequate ignition with flintlocks, you have to use real Black Powder in the flash pan, and a "Starter charge" of black powder in the barrel- sufficient powder to reach the vent, or Touch hole. The company used to recommend using at least 10 grains of Black powder, poured down the barrel first- not mixed-- and then your chosen volume of Pyrodex P, having subtracted the amount of the starter load from that total amount of powder. I don't know what their website now recommends, or if it continues to be advised in their literature.
Why bother? You have to buy real Black powder to get Pyrodex ( P or RS) powders to work in flintlocks, so why not just stick to Black Powder for the entire load? :hmm: :surrender: :hatsoff: