I've just come across a Collath patent shotgun side by side. The long under-lever locking mechanism looks like Lefauchaux at first site, but is based on an eccentric cam.
I have a short but quite good article about Teschner & Collath (owner and workshop manager respectively) of Frankfurt an der Oder, from the German Gun Collector's Association, also a reproduction copy of a T&C shop catalogue of circa 1914.
it looks to be 12 bore, but in common with many makers of the last two quarters of the 19th century, T&C also made the own cartridges of differing dimensions under the delightful name of TESCO - I joke not.
Anyone else come across them?