Not enough photographs to understand what you have. My first guess is a Snider Enfield action made into a shotgun. You can take a look at this video, see a Snider action, and all the marks in places you are not showing.
But, there were other flip type military actions floating around. In the period prior to WW1, it was not uncommon to convert old military actions to shotguns.
Frank De Haas's book on Bolt Actions has a whole section about post WW1 Mauser actions converted to shotguns. I know I have a 1902 Sears catalog in which Sears is selling old military flintlocks, described as suitable as a shotgun.
So, with more pictures of more proof marks, manufacturing stamps, someone out there might recognize your particular shotgun.
Might take a chamber casting to figure out what you have, but I sure would not fire any smokeless loads through it. Cheap shotguns like that were made out of the cheapest materials, and if this is a blackpowder era conversion, it will not be safe with modern shells.
