I was given this and wondering what it was fired from !
Your trench art piece is most likely made from a German 77 x 230mmR cartridge case (what is the diameter of the case rim?).
Produced by Polte Werke, Magdeburg, in December of 1915.
“St” indicates a reinforced (stronger) cartridge case construction.
“172” = serial number
“Sp252” identifies the inspector for quality control.
This cartridge case was used in the German "7,7cm leichte Feld Kanone (l.F.K.) 96 n/A " or 7.7cm (77mm) light field cannon, 1896 new model.