[Jim K]

Got me. If it is supposed to keep the pan dry, waterproof pans were in common use before that pistol was made. If it is supposed to keep the powder from falling out, the regular frizzen does that and has to be closed and the pan covered before the gun can be fired. Pan covers were common on matchlocks and snaphaunces but it doesn't make a lot of sense on a flintlock.

If it is a safety, it is a rather crude one and looks like it would be hard to move out of the way in a hurry. The normal sliding safety was more efficient and most were automatically kicked off when the cock was pulled back. That one would have the advantage of being installed with only a change to the frizzen, no alteration of the lock would be needed.

Jim