Hi Charley777,
I think your cases are 7.7cm Manoever Kartuschen, which are usually very early 7.7cm cut down cases, this being very well made and the inside of the case being lathed, however they usually are 100 mm long, not 135. When the 7.7cm Field Gun was introduced in 1896, casings were very expensive and always reloaded several times, some were then turned into Manoever Kartuschen or wooden drill rounds.Chances are you will find several reloading marks on the side of the rim, usually up to 10 or 12. I'll be curious to know how many times yours were reloaded.
Frank