https://www.abebooks.com/9780891490067/Standard-Directory-Proof-Marks-Wirnsberger-089149006X/plp
Standard Directory of Proof Marks - Wirnsberger, G.: 9780891490067 - AbeBooks
On every important part of every shoulder gun or handgun sold in Germany is a small mark. This is the mark of the proof house where the gun underwent proof....
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