I hunt with drillings a great deal and hunted in Germany for a number of years and there is no "usually" about it. The scope is only for the rifle barrel and perhaps for a .22 insert barrel for the right shotgun tube should you have one. It is also why a drilling was/is always equipped with a dismountable scope system such as claw mounts so the hunter can shift from scoped rifle to true shotgun and back quickly and with no change of rifle point of aim. If you scope it, do it for the rifle, and do it with quality mounts.
