With some of the newer rifles that claim to shoot pellets, they will shoot Pyrodex Pellets therefore they would shoot loose Pyrodex but to be honest, Triple Se7en and Pyrodex all have a lot higher flash point then Goex Black Powder. With a flint lock the spark and flash point are what makes the ignition fast (from all my reading).

If that is all you can get, then try it. In the mean time keep looking for some real black powder. I have used Powder Inc. and they are great to do busines with, fast, and reasonable. Get one pound of the 4f, and then the rest in what your rifle likes. I personally get it in larger amounts and of different grades for different rifles....

Using anything other then Black Powder in the flash pan I think will cause some real problems. It might work but I do not think you will be happy with the speed or results.... Get some black powder....

good luck