Trying to identify this (assumed to be) ammunition box. As you can see its dated 1916 but I can't find out what the other markings donate. The top of the box has a large copper sliding lock with a nut in the centre. This turns and the copper slide moves along the lid and locks into the four brass pins which protrude from the main box into the edges of the lid. It's very unusual and can't find anything similar despite trawling the Internet. Any help appreciated. Thanks