You have already identified it as a Shapleigh's King Nitro. Shapleigh Hardware was in St Louis Missouri from the mid 19th century until the middle of the 20th. Their King Nitro guns were manufactured by W.H. Davenport and later by Stevens/Savage.
I HAD AN OLD GUN SIMILAR TO THE ONE YOU ARE TALKING ABOUT AND IT WAS MANUFACTURED BY A COMPANY CALLED SHAPLEIGH IF MY MEMOERY SERVES ME CORRECT Is it a windmill or possibly the Perone, an oblisk similar to the Washington Monument? That would be a Belgian proofmark. Shapleigh was a hardware wholesale/retail business that had its tradename guns manufactured by several manufacturers. "Nitro" would indicate the gun could safely fire the smokeless or white powder which was developed around 1900.
The best that I can do is say that the Lefever Nitro special was made from 1921-1948.
HAVE IT CHECKED OVER BY A GUNSMITH FIRST!!!!!!!!!!!! It is an old shotgun.
The Lefever was mfg. in 1935.
older than you
Known tradename used by Shapleigh Hardware. The guns were made by several different manufacturers, although your double is probably a Crescent. 1900-1930.
Your shotgun was manufactured in 1923, by Ithica Guns which took over the Lefever brand when they acquired the corporation in 1916.
The shotguns were manufactured by Ithaca from 1921 through 1947. Yours was manufactured in 1928.
My Triumph shotgun is seventy-six years old.