What you have is a casing from a [77mm German field artillery piece][1], possibly like this: [![enter image description here][2]][2] Some of the stamps: - St: Strengthened case - HL: Haniel Luege Düsseldorf (brass factory) - 25: Inspection Mark not sure yet on the G([may indicate][3] maker *Geschossfabrik*), and 36 may be lot number. März 1917, of course, would be the date. ---------- some sites to look: - [Large calibre markings on cartridge cases][4] - [Great War Forum-German Shell Case Markings][5] [1]: https://en.wikipedia.org/wiki/7.7_cm_FK_96_n.A. [2]: https://i.sstatic.net/2VJNv.png [3]: http://1914-1918.invisionzone.com/forums/index.php?/topic/28930-shell-cases/ [4]: https://ator1149.home.xs4all.nl/wfm/ww1/ammunition2.html [5]: http://1914-1918.invisionzone.com/forums/index.php?/topic/160019-german-shell-case-markings/