The monogram on the eustucheon looks like "ATGC" in an Arts and Crafts Gothic sort of script. The hook of the G making the crossbar of the A. If what I think is an A were an H, the tops of the uprights would not touch probably.

One of those maddening little pieces of provenance that would be almost impossible to identify without a gunmaker's sale book or a freak of luck. I have an early scope case with something very similar on it, equally unlikely to ever be ID'd.