The following advertisement was found in the 1905 edition of Deutsche Jagd und Deutsche Fürsten by fritz Frenzel

The following images of a Collath gun that is a two barrel set are courtesy of Mr. Fredrik Franzén in Sweden.

Following are more images from Fredrik Franzen of a W. Collath double rifle with a Clam Shell (Mussellverschluss) action.

The following images are courtesy-