For the uninformed,,,
Dreilling is 3 barrels
Zweilling is 2 barrels
Drilling is three barrels, not "Dreilling". The word literally means "triplet".
The corresponding word for "twin" is Zwilling, not "Zweilling", but I've never seen it applied to firearms. Two barrel combinations are named by the layout, for example a Büchsflinte is a shotgun and rifle, side by side. A shotgun and rifle combination over and under is a Bockbüchsflinte. Two rifle barrels, over and under is a Bockdoppelbüchsflinte, though a light version with two rifle barrels of different calibres is commonly called a Bergstutzen.
