cayugad

I would say Pittsburghunter might might be on to something. What you're getting is a fuse effect. I never put more then 3grains of powder in the pan. That is one set with the small pan flask. I like to stick it away from the vent liner along the back side/outside edgeof the pan.

Also are your running a vent pick into the vent liner before shooting. This does a couple things. Not only does it make it clear so the spark can get to it, but it also drags just a very small amount for the main charge towards the vent hole. So when the spark hits, it explodes instead of smolders.

Be sure your pan is dry and oil free. Try reducing the amount of powder in the pan. Try placing the powder in different parts of the pan. Pick the vent hole. An easy way to do that is put the vent pick into the vent hole and lower the frizzen pan lid on the vent pick. Then pour your main powder charge down the barrel and load the projectile. Now your ready to prime the pan, and you open the frizzen lid and remove the vent pick. This insures that the vent is open and the charge is ready to accept spark.

Also the importance of a sharp flint can not be over looked. Where are you getting your flints from? Have you ever tried an Agate flint? You will just have to play with it until you find the right combination. Those are nice rifles. I almost bought one when he was closing out the models that the breech plug did not come out of...