The flap of this cartridge box was probably made with a rounded shape, common on such boxes made early in the Revolution. At some point it has been cut into the current scalloped shape, while at the same time shortened in width. Late in the Revolutionary War cartridge boxes with scalloped flaps became more popular, a feature which persisted into the 19th century. The owner of this box may have cut down the flap in imitation of those styles.
Saddlers and harnessmakers often made simple cartridge boxes like these for American soldiers in the Revolutionary War. The box itself is just two D shaped pieces of leather sewn together with waxed linen thread to form a bag. Sitting inside the bag was a wooden block drilled with holes for cartridges. A larger flap to cover it was sewn to one of the edges, and a shoulder strap sewn into that seam. The rounded wooden ears nailed into the side of the bag were probably added later to make it more secure against rain.
Using pre-made cartridges a soldier could be trained to load and fire his musket in just 20 seconds, far faster than using loose powder from a powder horn. Cartridges, however, were made of paper and could easily become wet and useless. By the late 17th century leather boxes with wooden blocks became the standard way to carry the effective but fragile cartridges.
The wooden block inside this leather bag has 19 holes drilled into it to carry pre-made paper cartridges. Boxes like these were common in New England and New York early in the Revolutionary War, and have even been recovered from the site of the Battle of Valcour Island in Lake Champlain. The Federal militia act of 1792 ordered American militiamen to carry a box with a minimum of 24 rounds of ammunition. Some older cartridge boxes have inserts added to carry the extra rounds. This box has no inserts suggesting it may not have been extensively used after 1792.