This Winchester 9mm 50 Cartridges Box for submachine gun only is a reproduction of an original cardboard ammunition box used during WWII. The ammo box is empty.
This particular ammo would have been manufactured for use with the 42 SMG. It appears to also have been supplied via Lend Lease for use in the British STEN gun.
The Winchester submachine gun ammo box appears as part of a British Paratrooper’s kit in The D-Day Paratroopers, vol. 2 by Jean Bouchery.
The second photo shows the side by side of our original box next to our reproduction.