In the case of a collectible firearm, a HUGE part of the value is based on condition and originality. It is impossible to offer a value without a hands on appraisal of the firearm. You need to find a dealer in collectible antique arms to examine the gun, and give you a valuation- it is simply not passible at long distance.
The value of a double barrel Harrington Richardson 1900 20 gauge gun depends on its condition. This gun in excellent condition is valued between 180.00 and 240.00 as of 2014.
Blue Book of Gun Values will help.
A Gun Play in the Klondike - 1900 was released on: USA: May 1900
Gatling Gun Drill - 1900 was released on: USA: May 1900
Steel or Damascus barrels?
Value of any gun is based on make, model and CONDITION- which you did not give us. Value could be anywhere from $25 to $250.
The price for this gun 165000 euros if it has 1900 carving on it and in gold.That is the lowest price!
Blue Book of Gun Values
TRY THE BLUE BOOK OF GUN VALUES FOR PRICES..
You can't value anything with just a serial number. Who made it? What condition is it in? Is it a hand gun or a long gun?
This shot gun in good shape with the word Long Tom clearly on the side of the gun. will be in the 500.00 to 600.00 range.
Check out the auction sites - Gun Broker, Auction Arms, Guns America. Condition is the main factor.