A recent post on a very nice Geco 7.63mmM box (hst "D Geco D 7,63 ) encouraged me to write this post. It reminded me of this box and cartridges owned by a collector in Germany. I believe this is a quite unusual headstamp on most calibers, and extremely difficult to find in 9mm Para (it is rumored to exist but I have not confirmed that it really occurs on 9mm Para)! There is a 9mm Para headstamped “GG&Co . D. .” which does exist but may be pre-WWI or even WWI vintage. I have seen this headstamp but don’t have one.
I speculate that the Geco headstamps of the 1920s and 30s began with the “D star star” headstamp below. This is probably the mid 1920s because it is found on 7.65mm Para cartridges but has never been documented on 9mm Para, nor with a Sinoxid primer as far as I know. Then the GG&Co headstamp above was adopted for a short time before the the introduction of Sinoxid primers. This headstamp was followed by The Geco D 9m/m D and similar concepts just before the full use of the Sinoxit primers (see https://forum.cartridgecollectors.org/t/date-7-63-mauser-box/26996/4 . and then the simple Geco 9M/M headstamps.
Any data shedding light on the progression of these headstamps, or any relevant information would be welcome.