Impossible to answer without knowing who made it and what it is, i.e, handgun, rifle, or shotgun.
what is the value of a jukar black powder pistol 007806
What is the value of a 1850 colt black powder with ships engraved serial number33700
The value of a black powder gun made in Spain with serial number 31587 25 Cal is worth approximately $150. The exact value will depend upon the condition of the gun.
50-100 USD
100 or so
20-300 usd
50-275 USd
1200
10-100 usd
50-150
1-1000
10-100 usd