If this revolver truly is 1875 production, it likely had a 7 1/2" barrel originally, and walnut grips. So, the barrel might be cut or replaced. Grips definitely replaced, 1896 or later, as Eagle gutta percha grips were produced about 1882 to 1896. Grips appear to be true first generation gutta percha. To confirm, do they have a burnt rubber smell. Seems to be well put together, not buffed/not ill fitting parts, a grey gun, heavily used but not abused. If the barrel has been cut, it's likely worth $1,000 to $1250. If originally a 5 1/2" barrel, $1500 seems about right. The lack of a crosspin confirms this is a blackpowder gun.