Got this before my mate started polishing it up.
I can make out 3.7cm flak 18 along the bottom.
There are what I assume are extractor marks at the 9 oclock, the number 14 at the 12-o-clock and 1939 at the 3-o-clock. Above the flack 18 is a 4 digit number (6348) with a star after it. At the 5-o-clock is a Heers Waffen-ampt mark.