Bi-metal 7.7cm case

[Gspragge]

I expect that these are pretty common in the UK and EU. But i seldom
find them here. Hard to read the headstamps though.
I may try to clean the base a bit. It does look like a # 15 for 1915.

 

[Hoeksel]

Indeed pretty common over here (Europe). You see at 12 o clock the Rheinmetall logo, 15 is indeed for 1915 and I see the Sp (Spandau) acceptance stamp at 9 o clock.