"Whatsit" ?

[DonVoigt]

Originally Posted by schutzen-jager

also used in U.S. Pederson device -

No.
The French long is not the same, close but no cigar.

Schutzen,
I sit corrected, My 10th ed. of Cartridges OTW, makes no mention of the .30-18, at least that I can find, only the
7.65mm MAS(French).

I can see how a .30 x 18mm can be fired in the French long chamber, but not conversely.
The Length of the French case is given as 19.8mm.

Hence my statement that they are not the same, close.