I too thought it looked like a military headstamp.If it came from the factory,I would opine that they were using "overrun" cases from WW1 contract.Since there is no caliber marked, it would have been a good way to use 30-06 cases rather than scrap them.They would have been loaded after 1917, I would think after the Armistice,maybe 1919 or so.BTY,after DWM went under and RWS bought the assets;I bought RWS 7x57R ammo(in RWS boxes)with DWM headstamps.No factory is likely to throw money away.
Mike