The narrowness of the buttplate, while still being rather flat, and a sliding patchbox, are an unusual combination. It’s being called a “rifle” buttstock because of the cheekpiece, I guess. Like suggested, a wood identification test would help a lot. I’m not familiar with Scandinavian locks, so this looks like a straight up English lockplate to me. Given it’s not falling into the usual categories, it’s easy to consider it a composite gun made of various working parts. In such a case, no one part can date the gun as the lock might date decades before it was stocked up as a new gun. Just one possibility.
