The crossed lightning bolts proof mark tells us this gun was proofed, in St. Etienne in a finished state. Many are the Darne guns that I have measured barrel walls on that are at .050 MW at the critical 9” from the breech location. The heavy wall barrels were considered the best guns to shoot and use by the guys at the shop when I was there.

I have always wondered if the heavy wall thickness was insurance on a gun proofed at completion against the always heavy French proof?

Best,
Ted