It is quite clearly marked.
The "Nazi Buzzard" is a Kestrel surmounting a wreathed Swastika: the official insignia of the German Reich in the time of the National Socialist Government.
WaA 648 is the inspection marking of the Inspectorate Office which accepted the cartridge: Office Number 648. Records exist of which Office was stationed at which factory for the period.
38 is the year of production: 1938. Hitler didn't revive an ancient calendar or anything, the way Mussolini did. You don't have to worry about the year of the New Roman Empire - just use the ordinary Christian calendar.
P315 is the Factory Code, in this case the factory code for Markisches Walzwerk GmbH, Strausberg bez. Potsdam, Germany. They made quite a lot of ammuniton in the Third Reich years, being originally specialists in metal rolling.
35C is the drawing number which governed manufacture of this particular casing, just the same as drawing E37 governed the manufacture of brass-cased 7.92x57 for the A/C MGs. The original drawings still exist in one form or another and provide the complete specification.
It is actually a very complete headstamp.
Hope this helps.
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