MD...

WAAAAaaaaay too much powder in the pan!! That big fireball is a greater part of the reason you flinch. I've found what works best in my locks is a thin band of powder across the bottom of the pan. You want a flash, not an explosion. Something you could try at the beginning of each shooting session is to prime the pan but don't load a charge and practice shooting just as if the rifle was loaded. Try to keep your eye open while you practice, this can help you get used to the flash. AND... you should always wear safety glasses, especially with a flintlock. It would be bad enough having to quit hunting for a trip to the ER to have a flint shard dug out of your eye and risk partial or total loss of your vision!!

BPS