This is incredibly rare and highly collectible original Wartime German produced 7.92X33mm KURZ, also known as 8mm KURZ. I’ve seen examples of a single box (15rds) sell for over $300. It was used in the German MP44 and STG44 assault rifles. At the end of the war all the leftover unissued ammunition was relabeled by the Czechs with a 1955 label. Ammunition dates from 1943-1945 with a “dou” headstamp.