Silver,
Flintendrilling just means "Shotgun Drilling".The trigger sequence is the same as on a common drilling.What no one has considered is the use of a slug or buckshot(posten)in the bottom barrel.In this case,having to use the selector to fire the bottom barrel would be desired.This arrangement would be useful for drive hunts in the forrest.When I lived and hunted in Germany,shot was not allowed for hoofed game,but earlier it was.
Mike