Bruce and Dean, agree 100% to what you both said. The problem is getting use to or remaining focused when the powder in the Flash Pan ignites!
Over on the ALR forum a few months ago there was the discussion on how to deal with the flash in the pan / the inevitable flinch from same when it goes off.
The upshot of several pages of discussion was NOT to mention it to the new shooter, and to prevent the "OLD TIME SHOOTERS" from teasing/cautioning/explaining/preparing a new shooter about the flash in the pan.
If all the shooter is concentrating on is the sight picture, and follow through; which is ALL ANY SHOOTER SHOULD BE DOING, then the powder igniting in the pan will not be as great of a distraction as most people seem to think it will be!!!
And, that's how it was for me. With nothing but the Lyman Black Powder Handbook to guide me, no human mentors or tormentors, I did EXACTLY AS THE CONSENSUS AT ALR SUGGESTED.
I loaded the Golden Age Arms Company Lancaster longrifle, primed the pan of the Siler flintlock, and pulled the trigger without flinching. So did my friend Charlie.
We didn't have anybody telling us it was going to be a problem, so there turned out not to be a problem. IMAGINE THAT!!!
The other consensus to come from those pages of discussion was that once the flash in the pan was causing a flinch, to just try focusing on the the front sight. And, to REALLY FOCUS ON THE FOLLOW THROUGH. Swinging or moving targets might be helpful for follow through with a flintlock.
Edit to above:
I was fortunate in that I had saved up my minimum wage, after school job money, for over a year to purchase that GAA Co. flintlock at cost in 1971 of $330.00.
That got me a very well built, by today's standards, semi-custom longrifle. The Siler flintlock was assembled as perfectly as one could ask for. With one of the sawn German agate flints that I purchased on a whim, it sparked EVERYTIME I pulled the trigger.
And, a well functioning flintlock is a joy to use. I have been quite fortunate in my choice of builders for the 3 flintlock rifles, and 2 flintlock pistols that I had commissioned to have built in my past.