Very interesting find!
Never seen one (or even a picture) before .......

It is a cross between a Bugelspanner and a GEM, as it uses the barrel and cylinder system from a GEM and the cocking handle and stock from a Bugelspanner.
It is not a homemade project as the castings are specificly made for this model, and all parts are hand fitted and numbered with the cyfer "9" .
No indication of a manufacturer anywhere to be found, so can only take a wild gues who could have made it.
Eisenwerke Gaggenau, Oscar Will or Fritz Langenham spring to mind,but who knows?















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Frank