The museum in Switzerland has become a font of information I'd like to share. Not only does the conservtrix live in the same town from which Le Corbusier came - which is a short commute from Le Locle - she has come up with the names of several other gun makers living and working in the Neuchâte mountians area, which I will list here - hoping one may ring a bell with someone. I don't know if further info exists but if you're interested in any one perhaps the info can be had???
Chammel, Paul Edouard, born in 1825, from Prussia, gunsmith
Naguel, Isidore Joseph, born in 1825, from Prussia, gunsmith
Rychner, Henri, born in 1824, from Argovie (Switzerland), armurier
Kuster, Ulrich, born in 1827, from Saint-Gall (Switzerland), worker gunsmith
Sutermeister, Fred Moïse, born in 1815, from Argovie, worker gunsmith
Fessler, Justin François Adolphe, born in 1825, from Schwytz (Switzerland), worker gunsmith