Unknown stamp "Bis" on French 75x350 Schneider

[Hoeksel]

Although I do not collect WW1 shell cases, I could not leave this one.....I find the headstamp interesting. I do not remember ever having seen the stamp "Bis". Does anybody know what it means?

 

[RichardB]

With regard to French tank development, bis was appended to the name to indicate and upgraded version. For example the Char B1 bis, which was effective the second versions of the Char B1. There was also a Char B1 ter, which was the third version.
Quite how that relates to your case, and whether indeed it does relate to a second version, I can't confirm, but it might help point you in their right direction.

rich