Here the box and the pics of the ammo and headstamp,
green Primer seal, and packed in 1944!! (from the headstamp it was produced much earlier.).
But the packingdate 1944 goes conform with many other uncommon calibers packed by Gustloffwerke during 1944…possible a cleanout sale of stockpiled older ammo (like 8mm Lebel, 9mm Lefaucheux and many others)
here the pic