The only sheaths stamped on the flats of a Darne come from the proof house at St. Etienne. Since 1965, officially, and for many years prior, unofficially, a Darne typically was triple proofed. The circular marks stamped on the flats of a Darne mono block identify the grade of gun. The proof house has nothing to do with them.
There was a time when it was common to proof individual tubes for Darne guns at the proof house, prior to making up a set of barrels with them.It was called provisional proof. But, most Darne guns built since the war bear the crossed lightning bolts on the flats indicating it was proofed as a finished gun. If there is a Darne gun that bears just one of those marks, I haven’t seen it.
The sheaths stamped on a Manufrance gun that has been privately proofed look suspiciously similar to official French proof house markings.
Best,
Ted
