all truth. if it was an original 1863, it wouldn't be sitting in a barn. many/many reproduction models have been made and the value of the gun is determined by it's condition. new their 400-600,,uncleaned after shooting and left to the elements with in weeks could cause damage enough to devalue to 100 or less.
Some times the parts sold individually can be worth more than the gun it's self.
photo's and/or more info about other marks on the barrel like manufacturer, lock condition, butt plate, side plate, could help the board help you.