Mr.Greener called them serpentine fences,they were normally used on mid-grade guns.I have a self-acting ejector 10 bore that held it's own next to some clanking 3 1/2" twelve ga. autos,in the snow goose wars,last week in S.D.
Your serial dates it more in the late 1880's I think.I would like to here what your bore size is proofed at,Greener made some thin brass case guns in that serial range.