The black powder replacements are harder to ignite that true black powder. Read on the Pyrodex website that for flintlock arms to prime the barrel with 5gr of black powder prior to the main charge of Pyrodex. That and Pyrodex makes a crappy prime charge. 4F black powder works far better. For flintlocks it's black powder all the way. How do I know all this? I shoot a Brown Bess every so often.
In Louisiana we have a grand total of one, yes just one, licensed black powder dealer. Crying shame as the only black powder manufacturer in the US is located in Doyline, LA near Shreveport. Contact Judge Angelo J. Piazza, III at http://www.jackspowderkeg.com/. His honor is the city judge of Marksville, LA. A hardcore Civil War re-enactor and a nice guy all around.
The law has been on the books for a long time. During the last legislative session SB82 was introduced to ease the restrictions and allow purchase and possession of 25lb of black powder. However it was gutted in committee with pressure from the state police. End result that was signed into law is that if you are part of a recognized artillery unit of cultural re-enactors and certified by the state parks you can purchase and possess 25lb. For the rest of us it's still 5lb.
And do you have a contact in Bay St. Louis?
Black powder substitute, Pyrodex and the like, doesn't work well at all in flintlock arms. The substitutes are harder to ignite than true black powder. Even Hodgdon suggests to prime the main charge with 5gr of black powder prior to the charge of Pyrodex. That and nothing works better than FFFFg black powder in the prime pan.
In centerfire and caplock arms the substitutes work fine. The percussion caps and primers have enough oomph (<-- technical term) to ignite the substitutes. I see only two advantages to the substitutes over true black powder. 1-The substitutes are widely available and 2-You have more wiggle room prior to cleaning the guns. With true black powder you have about 3 hours to get them cleaned in our environment.
