Im no expert on German proof marks but maybe......
12.7 mm would be .500 caliber.
70 mm would be case length of 2-3/4".
And the 36gr would be 36 GRAMS rather than grains and would be a bullet weight not a powder weight.
36 grams equals about 555 grains I think.

Could this bullet weight have been used as a proof weight rather than the actual cartridge bullet weight?