12 gauge Damascus with hammers

[James Milroy]

My late father showed this to me over 40 years ago, from his closet. I think it was his grandfather's shotgun. My dad never fired it during my 50 year lifetime (he may even not ever fired it himself…I don’t know)....I recently found it again in my mother's closet. I don't know much more about it, but it looks to be in remarkable shape for its age. I don't know if it is worth $10 or $10,000. It appears to be 12 gauge. My grandfather's surname is carved into the bottom of the stock. Little "curly Q's" are all over the barrels in the bluing...I tried to capture that in a close up photo. The triggers and hammers work well, and the action is tight/solid. The barrels are 30 inches long, and look "wire wound" inside, but not overly corroded or pitted. On the bottom it says Pat'd Mar 23 1875 and Nov 13 1866. On the lower action it is stamped 15828 and the matching 15828 is on the upper action. Other than wiping the many decades of dust off of it, I have not tried to take it apart or do any "ignorant restoration." What year might this have been made, and does it have a name/model?