It will be awhile until I am back in my office (over a week) and I do not have access to posting pictures on the road. That said until then, the Jules Bury proof mark is a JB under a crown. It normally (at least on five examples I have seen) appears on the water table of the receiver.

I found an example on the littlegun website


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None of the Jules Bury made Louis Christophes barrels I have have seen have any JB markings they are all marked HY Andrew Toledo Steel Works

Michael Dittamo
Topeka, KS