Hi Fiftyfour,
The pan is about 3/16" from the end of the barrel because the vent hole has to clear the breech plug. Of course it is correct. On some locks, the pan is large such that the fence is lined up with the end of the barrel. That is not the case with this lock. No, I am not referring to any thickening in some lock plates. All locks have a thick bolster, which is the metal you drill into for the rear lock bolt. The shoulder on the flintcock rests on that bolster when the lock is uncocked. To make clearance for that shoulder, you either do what I did or you cut a notch in the stock behind the pan. I do not like those notches and have never seen one that looked good although there are plenty of original guns with notches cut. I avoid the notch by slimming the lock panel flat to the point where it almost disappears, like in the photo, and also shaving in the wood of the lock mortice inward as it approaches the pan so more of the top of the lock bolster is exposed above the wood. That way enough of the top of the bolster is exposed such that the shoulder of the flintcock can rest on it without touching the wood. Hence, no notch is needed and it all looks much nicer.
dave