BTW, there was indeed a shotgun proof in Belgiun from 1924 - 1968 called fourfold, the marks were a crowned EL with laurel branches for treble bp proof of the barrels and a crown over PV for a higher than usual smokeless pressure load.
Not sure on the term fourfold there Axel, but do you mean threefold per the triple proof on the unfinished tubes?
Triple Provisional Proof
Double Provisional Proof
Then there some bastard of a proof referred to as superior.
Auch
There seems to have been a gap in this so called superior proof form 1924 - 1959 and the mark was, that is if the 2 superior proofs were one in the same.
Kind Regards,
Raimey
rse
