4000 Atm test(4000 Atmosphären-Pulver) - you may be thinking of that.
Post 1912(1911 - Z-M) Eagle Nitro(block) noting tube for shot passing thru Suhl proof facility while the stamp of Eagle Crown over N Nitro(script) notes a tube destined for shot passing thru the Z-M facility. Early on, say 1912 - 1922 typically the postion of the Nitro is on the sides of the tubes. Post circa 1922, you will find them on the lower flats. Pleasure us with some images of the Crown over B(experienced proof in final state) & the other N on the water-table. It surely dates from 1912 - 1922 but I'm fairly confident it was made in 1911-1912.
Kind Regards,
Raimey
rse
