Originally Posted by Argo44
I believe Douglas is referring to this mark:
[Linked Image from i.imgur.com]

Here is a line on Charles Osbourne & Co.
https://doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=428703

Since it's been re-barreled, wonder whether the number on the fore-end 18395 might be the original Osbourne SN? Usually if that number is under "Patent" it indicates Patent Use Number (PUN). If this is an Osbourne SN Lagopus will help date it.

Charles Osbourne catalogue from probably 1890?
https://campaignfurniture.com/artwork/chas-osborne-co-gun-catalogue
See the picture of the harpoon gun:
[Linked Image from i.imgur.com]

It makes great sense for it to be made by Charles Osborne, a huge remaining question is setting a date?

The 19395 Patent was presumably ended i 1910, furthermore I've found another shotgun with the same John Ross ejectorpatent but an earlier usenumber being 400, this was built in 1896(circa) - meaning the original gun was probably made somewhere between 1896 and 1910.

Niels Johann Holm Jacobsen