In very good condition it would be worth thousands of dollars. Poor condition, probably not much if anything. Ernest Dumoulin of Leige, Belgium made many hand built box lock doubles.
Damascus barrels were state of the art for their day but are UNSAFE with modern ammunition! DO NOT SHOOT this shotgun with any ammo of any strength.
In life, strive to take the high road....It offers a better field of fire.
"Robo is right" Fuzzball