Raimey,
sorry for cutting off the "Bhler"! Look here:




No more marks on the standing breech, bushed firing pins.
There were marks on the barrels but no more visible.
The Rhombus mark should be interesting. The gun was marked on top of the barrels with the name of a small guntrader in the nearby city of Hameln, Lower Saxony.

Best Regards,
Wolfgang