Nitro King was a trade name sold by Sears Roebuck and H&D Folsom Sporting Goods. Manufactured by Crescent Firearms, Norwich, CT, c. 1905-15. You can invent any history you want for the last 90-100 years, 'cause no one was keeping track of it. It most likely has fluid steel barrels and could still be used as a field gun, if approved by an experienced gunsmith. But if it has a side-hammer, it probably also has a twist-steel barrel and should be a mantle decoration now. Should be worth about $50-$75 for either use.
50-100
Seldom exceed 150 USD
50-100 USD
50-100 or so
Single barrel, tops out at $75. Double-barrel, tops out at $175. sales@countrygunsmith.net
I believe that King Nitro was a model name of Shapleigh Arms Co, St. Louis, MO.
20-120 usd
50-100 USD
70-100 years
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.
BLue Book of Gun Values
50-150 USD