That ground up 2f should work fine as a prime. And the RMC vent liner IMO is the best touch hole liner on the market. I will not shoot a rifle without one. I am guessing the problem is the touch hole.

Next time you load.. get some fuzzy pipe cleaners. Push one of them into the touch hole then close the frizzen. Now load the main charge and ball as normal. SLOWLY pull that pipe cleaner back out of the touch hole. What this does is drags powder with it, right to the back side of the touch hole.

Some rifles like their pans filled on the outside of the pan, while my Lyman GPH like the powder close to the touch hole. You have to experiment. How are you putting the powder in the pan? Just tapping out of a horn? If so, push a little up near the touch hole.

Also a sharp flint is important to good ignition. It creates long hot sparks. Also what some call a hang fire, other do not. But you're experienced enough to know the difference. And you're sure the bore is nice and dry when loading.. So like you said, just keep playing with it and trying it in different ways. Soon it will start to fire.

A well tuned flintlock is as fast as a cap lock and as dependable too. One reason I guess I like flintlocks.