I have been searching a site for some time now and found lots of 20mm cases in various conditions with dates ranging from 1941 to 1943 and various makers. I have found one today that I consider the best of the bunch, it has a ink stamp on the case that says :- 20mm M21A1
DURA EDH-3- 1 6 0
It has a smaller ink stamp underneath which is illegible.
I think it's amazing that this case has been in the ground all these years and the ink stamp has survived. Also this particular case has no maker mark or date stamped into the bottom of the round as per normal. Can anyone out there who knows about these cases tell me why? Is this a unusual case or was his the norm?