Re: Rifle that will not fire ????
I suspect that a percussion cap is not "hot" enough to ignite the "sticks" reliably.
I have never used any Pyrodex product because it typically produces less velocity for a given charge than "Black Powder". If Hogddon says "No", I am not going to recommend otherwise.
I would get a pound of "Black Powder" or the recommended Pyrodex grade.