Ammo can or ammo box?  Technically the ammo can is air tight, disposable and has a tear off strip.  The can has a key attached and is opened like an old style coffee can. The can cannot be resealed.  An ammo box (sometimes referred to as a chest) has a hinged or removable lid with a rubber gasket and can be resealed.  The lids of most ammo boxes can be removed.

Prior to WWII ammunition was carried in the field in wooden boxes.  These were neither dust proof nor moisture proof. Ammunition shipments overseas were usually packed in airtight cans or metal inserts in wooden crates (terne-plate liners) and removed when they arrived in the battle area and transferred to boxes. This was inconvenient and there was a need for containers that could be shipped and be immediately ready for use.  Early prewar metal boxes like the M17 had no rubber seal. Later metal ammunition boxes developed for WWII were dust and moisture proof. There were several types and sizes depending on the type of ammunition. 

Boxes and cans have been divided into two sections here, World War 2 & post World War 2. Click on the button below to go to either section.