Hi Andreas,
What a beautiful rifle! I cannot tell if it is walnut or maple. If walnut, it is clearly a dense piece. Folks should be careful about assuming a gun stocked in maple had to be made in North America and not Europe. Maple burl was commonly used during the 17th and 18th century by English, French, and German gunsmiths, particularly for high-end pistols. Espingarda Perfeyta describes using maple but strongly recommends walnut. Good wood became increasingly rare in western Europe in the 18th century as most of the old forests were cut down for lumber,fuel, and farming. Europeans imported a lot of wood from eastern Europe, North America, and Scandinavia. In fact, the present state of Maine was mostly a British Admiralty forest reserve to provide large pines for ship masts. It was a matter of national security for England because big trees were so rare in England.
dave