JG3 and 7 September 1942
 

This question is regarding an item of trench art: a 20mm brass cartridge case with a stylized JG3 unit insignia (winged-U and axe head combination), the date 7.IX.42, and "GUMRAK" entered (hand etched). May this relate to any particular or notable event involving the unit's operations near Stalingrad on that date?

Thank you,
Steve