What is "tuning" the flintlock?

[paulvallandigham]

I have seen the pictures and talked to Pletcher about this. While the main charge fires the ball down and out the barrel after the hammer finishes its fall, ignition of the main charge begins before the hammer stops. When the lock is tuned just right, it does occasionally fire before the cock finishes its fall. I know this has happened with my gun on more than one occasion. And its been witnessed by other shooters watching to see it happen. Not all locks work this well, and a lot of factors have to be in play for this to happen.