Here's a very nice box of Federal Monarch shells from the early 1940's (1942-1945) which were sold to the US Government during WWII. You will note in the second picture that the warning, later found on the secondary flap of the box, is on a seperate piece of paper.
These are rarely seen today, for obvious reasons, but it appears this box had not been opened until I did so. The patent information printed on the shell heads was discontinued after the war too so several little details help to make this box a little different.
The shells themselves are different too. Many Federal shells made during the war had bright steel heads but these appear to be brass. However, they react to a magnet so are either brass washed or have a steel liner in the base (commonly found on Remington shells circa 1905).
While perhaps not "rare" all these little points make this an interesting find. Similar boxes, empty, have sold for $40 and up while some are listed for as high as $150!
(The mallard box is very popular with box collectors.) I bought this one for $25 at a gun show and felt like I did rather well. Happy collecting!