The value of any "Antique" is always a very subjective opinion.
research what a similar item has sold for and you will have your answer.
Around US$ 2,000 depending on its conservation status. Without DETAILED descriptions the range could be 100-10000 USD or more. While they may be old, a 1900 rifle is NOT legally an antique. US law has a specific legal definition of antique firearm, Unless they are muzzle loading guns, they must have been made in 1898 or earlier to be an antique. Values will be based on specific make, model, condition, and originality. without detailed information, we cannot even make an educated guess at value.
Without seeing it, I would guess that the antique value is nonexistant. The name "Danial Boone" is unrelated to the American frontiersman and is only there to sell the shotgun. It is possible that the gun is American manufacture (Crescent City made thousands of inexpensive shotguns with every name brand you could imagine) or it could be a Spanish or Belgian shotgun. In any case, it is not a Purdy or Winchester or other brand which would command "antique" value. If the gun functions, it would be considered a field piece and could be worth a few hundred dollars. If it is worn out, it is a wall hanger and would not be worth the cost of restoration.
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