TW,

I agree with you, for a three smooth barrel gun(flintendrilling) there is no need to operate another lever/button to select a barrel of the same nature as the other two. After all, one shoots the three shots at the same or same type of quarry. That is the reason for my initial question. For a drilling it makes sense to have to operate another lever/button in order to change the "mode" of the weapon according to the quarry.
This makes me think that my flintendrilling is either built on a drilling action, or there might be something wrong with the trigger mechanism. Does anybody have any opinions?

In a different order of ideas, is it possible to change a drilling to a flintendrilling by switching the rifled barrel with a smooth barrel using the same original action?