That patent date indicates it was made by Stevens/Savage. In NRA Good (won't be able to grade any higher if refinished) should be worth around $200-$250 retail. Being a 16 guage may lower the value in some parts of the country.
50-100
Seldom exceed 150 USD
50-100 USD
10-100 USD. Yes, any of the major wood shops should be able to make one.
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