Kimball Pianos with a serial number of 480000 or lower are pre-World War II instruments. Specifically, this one would have been produced in 1939, less than 4 years before Kimball would put a hold on production until after the War.
Impossible to value with just patent dates and a serial number. A DETAILED description of ALL markings, features, finish, condition, barrel length, sights, box, papers, accessories, and caliber are needed.
The serial number isn't correct. If it starts with an"8", it was made around 1916. It should only have a 5 digit serial number,though. It's worth $500 and up,depending on condition,markings,and history of the gun.