O/U or SXS, Brake action 6.5 G.

[Trooper]

In German guns it is often the case that the with a SxS shotgun/rifle combination that there are inserts for optional calibers. Same for drillings.

There should be inserts for a 20 ga. barrel for a 6.5 Grendel.

http://www.keppeler-te.de/cms/pages/engl...arrels.php

http://www.mcace.com/shotguninserts.htm
http://shotgunadapter.com/