U.S. Cartridge Box (Leather) 

Issued at the beginning of the civil war with a stamped  U.S. box plate and eagle breast plate. 

Towards the end of the war, cartridge boxes were issued without  brass plates as a cost saving measure. The letters US were embossed on the leather flap instead. 

Open view

Shows two tins that  hold 20 paper cartridges apiece. The inside pouch was used to store items like a vent pick or combination gun tool.