Lugercollector,
9K.M.C.1.1. is a wartime formation and not stamped according to the regulation. This unit mark is in my opinion a munition column of the heavy artillery.
Here are some listings from my archive.
9.Kurze Marine Kanonen Batterie (42cm)
9.Schwere Kuestenmoerser Batterie (30.5 cm)
9.Schwere Kanonen Batterie (15 cm)
"9K.M.C.1.1" = Ammo column 1 weapon # 1 of one of the above listed batteries.
Source : Geschichte des Deutschen Heeres im Weltkrieg 1914-1918. Das Ehrenbuch der Deutschen Schweren Artillerie. Feldgrau, ZfH.
Klaus