Would it be safe to say the earliest when it was proofed in 1923, latest in 1940?

Salut,

Cette arme est postérieure à 1963.

En 1964, le banc d'épreuve change son unité de mesure en passant du kilo au bar.

Fab,
Merci’.

Best,
Ted

Translation:

Hello This weapon is post-1963. In 1964, the test bench changed its unit of measurement from kilo to bar.

Oh sweet!! Thank you guys!!!

Lovely tid-bit of info...

Serbus,

Raimey
rse

Como asi la belle femme, porque non mon ami?? Le Reynard

Je suis en retard. Merci FAB. Interesant.

There is a very good site, shotguns.se/html,by Tobias Hassel of Sweden. One section of his site deals with the proof marks and details of various countries. France, England, Spain, Italy of course but many others including Germany(pre-war, post, East, West and after unification) and etc.

There is a book: Standard Directory of Proofmarks by G. Wirnsberger

which is the most comprehensive guide I have seen. I don't think it is still in print, but seems quite widely available.