Sam, the 9'3x72.12'1 gMG would be as you say for proof with a 12.1 gram Metal jacketed bullet. Difficult to see the small g. It would pair with the Eagle over I/J(repair), Eagle over N(Nitro), 1140 & Escutcheon of Carinthia to form the basis of reproof effort in Ferlach under the June 1st, 1939 German prooflaw. That would explain why it has 2 Ferlach crowned shields which typically note experiencing 2nd proof. So the preliminary datastring 7136.12.15'8.8'4 would have been early in 1912 with the 15.8mm and 8.4mm noting the diameter at the 1st pass. What are the stamps on the water table? And where is the weight stamp for the tubeset?
Kind Regards,
Raimey
rse