Bonjour Larry,
Riffling through some Mournetas books I have been lent, it is mentioned in all of
them, as you say, that a crown over F is: "épreuve ordinaire des armes finies à la
poudre noire", i.e. normal St. Etienne black powder proof for finished guns. Also
mentioned: Poudre noire dit "Forte", black powder called "Forte", thus the "F".
Proof Charges for 12 bore by decree of July 10, 1897:
10 grams of black powder "Forte" and 70 grams of shot.
Also mentions, as you say, that a crown over "S" is "épreuve superieur des armes finies à la
poudre noire" not to be confused by a crown over PS that denotes proof using
powder pyroxylée "S". This leads be to believe that the "P" does stand for Pyroxylée.
JC
P.S.: Here is an old Gastinne Renette with the black powder & Paris? proof:
