One of the Germanic countries for sure, past that or exactly where beats me. I'd vote for original 1/2 stock as well, I have a German fowling gun done the same way, except mine has about 4" of rifling at the very funneled muzzle, no riflings farther down. Lots of cast off eh? You could shoot around corners with that much! I like the sheet brass buttplate too, you'd expect to see a cast one. I like the cheek carving as well, would look gun on a contemporary "early colonial gun".
Thanks for sharing.