It is for the 7,5 cm leichtes Infanteriegeschütz 18 "le.I.G.18". The cases came in brass and copper washed steel. Yours is the later hence the "St" abbreviation after the casing number "6341". Steel cases were the most common, made from 1937 onwards as copper/brass were strategic metals and not used for common artillery cases if not necessary. The "P" to the left of the primer was the Firm Stemple for "Polte" one of the largest if not the largest manufacture of artillery casings. The number above the primer was the lot number of the case drawings.
The letters below the 6341St are the abbreviation for the name of the field piece. small letter "L", capital letter "I", (looks like a capital J) and capital "G".
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