I am the most unqualified person to answer but here’s a few observations.
Pictured is photo I took two minutes ago. I poured a small amount of Pyrodex P onto my Formica counter top and with the back of a t spoon reduced it to powder. Left side of the photo.
If that doesn’t fire under your flint lock your SOL.
As to fouling, again no expert but ??? Your not going to store the pistol loaded nor are you going to not clean it properly after firing. Fouling a moot point on both accounts.
As to snarky comments on subs in muzzle loaders, many here use them, some are actually superior in performance to the real thing, and due to Federal restrictions much easier to obtain locally.
I obtain black powder in bulk by on line order, simply because I shoot lot. The jar of Pyrodex pictured is close to twenty years old, it’s a hold over from when I shot only occasionally and bought it locally at a LGS.
As to forum location perhaps a mod will be along directly and move it to its proper subject location.
