Did some searching, I,ve always wanted to know myself. Pweeh! confusing!

There,s an old Gent on a French forum (I always trust the old boys) states it as Pinchard Denys, Norm

Confusing because apparently at some point two makers used the same code.

Maybe the answer is in the underscore on the S?

Here are the stamp mark codes:

AMS Workshop Loading Mills

ATE Building Workshop in Toulouse

ECP Central School of Pyrotechnics, Bourges

PD Ps Artillery Park Paris

Px Atelier de Puteaux

SFM French Society of Munitions

T Pyrotechnics Maritime de Toulon

APX Workshop Construction de Puteaux

The Pyrotechnics Maritime de Lorient

PDP Park Artillery Place de Paris

Mons Ste ESF French Society of Munitions

AMS Atelier de Chargement de Moulins

ATE Atelier de construction de Toulouse

ECP Ecole centrale de Pyrotechnie, Bourges

PD Ps Parc d’Artillerie de Paris

Px Atelier de Puteaux

SFM Société Française de Munitions

T Pyrotechnie Maritime de Toulon

APX Atelier de Construction de Puteaux

L Pyrotechnie Maritime de Lorient

PDP Parc d’Artillerie de Place de Paris

Ste Fse Mons Société Française de Munitions

I think these markings are based on a manual dated 1909.