You will be hooked when you pop your first with a flintlock.
That will clean right up with a little effort. And the scratches look like an old style hammer. Also that vent hole is the small one. The RMC makes a real nice one. I have the same rifle and it has a fast lock time. Check that Frizzen spring and make sure it break open nice and clean. It looks like it might be sticky. But even a new frizzen is not that much.
I got a GMB 21 inch fast twist that fits mine, and that has to be one of the sweetest little carbine rifles I ever shot. Although my original 1-48 barrel shoots roundballs excellent. Sounds like I might have to shoot that tomorrow...