A friend in Germany recently sent me the following photo. I have the same cartridge in my collection. I obtained it in 1995. At the time I was told that it was a Geco experimental. Note the half jacket inside the casemouth. This jacket takes a magnetic so it probably GMCS. the overall weight of the cartridge is 181gr so it is probably a 115gr bullet. The headstamp is Geco 9mm Luger. The diameter of the lead projectile above the casemouth is about 7.5mm.
Can anyone tell us anything more about this cartridge? What was the purpose? When was it made?