http://www.aiolfi.com/vente/vente-milita...ysteme-dewalle/

"shotgun system Dewalle: double gun, 18 gauge, left "Dewalle Frères", right "patented in Liège". Length of the barrel: 78 cm, Total length of the weapon: 118 cm. It is a percussion weapon using the principle of superimposed charges (two charges per gun). Each barrel comprises two pistons, each plate comprising two hammers. These are actuated by a single double-acting trigger which first actuates the anterior hammer and then, with a second pressure, the posterior hammer. Dewalle was a gunmaker in Liège, worked around 1840 until 1862. The proof marks were made before 1853. The serial number (140) is very low. "