Buchsemann,
Looking at the stockwork I feel that the untypical features may reflect the ideas or wishes of the first owner, and this gun was "bespoken" in every detail.
By the way, what is the length of pull? Looks loong on the photograph!
Everything is "top notch" in this gun, engraving included - money was no concern when the gun was ordered.

Regulation of the barrels might be "as ordered by customer" as well and you have to try and find out.
But my first concern there would be to find a good load for the rifle barrels.

fuhrmann