In a recent thread about Spanish Civil War 9mm (which I cannot find with the Search tool) John Moss mentoned the “G B” headstamped ammo. John said that this was originally thought to be British (i.e. made by Greenwood & Batley) but was now known to be German.
These rounds are found in the normal anonymous green 50 round box with the Spanish label, as are the Hirtenberger, Dordrecht “* P * 1934” headstamped rounds.
Ironically, there is actually a British connection with both of these cartridges. In 1941 Britain had adopted the Lanchester SMG but had only started initial production of 9mmP ammunition. We purchased large quantities from the US, but also bought 20 million rounds from Bolivia and according to wartime British documents both the GB and the Hirtenberger ammunition were issued to the service, presumably from this Bolivian purchase, ex Spanish Civil War. The GB is mistakenly shown as being for the Italian Beretta SMG.
Recently, a group of Norwegian battlefield archeologists excavated the site of one of the crashed British Horsa gliders from the abortive raid on the heavy water plant in Norway, and one of the items they found was a round of the Hirtenberger 9mm.