Right shoulder strap stamped Wm Butterfield/New York with additional New York inspector’s stamp and Aug. 15. 1864 date.
Condition: Knapsack shows significant damage to upper left front edge with a large quarter-sized hole in front flap. Leather straps dry and flaking but complete and without tears. Minor inside verdigris, G+. Cowan’s Auctions http://www.cowanauctions.com/auctions/item.aspx?id=33771