this is the firing pin of my st-ettiene side by side shotty,same model as yours but in .16cal ,I shoot this old bird a lot and always use 50 grain's of black powder with a brenneke bullit,but I ask myself if this old lady can be used with modern 16 gauche ammo,old man be carefull in using this gun my friend
this could be a rifle that is made by one off the hundreds of gunsmith's that where located in the LIEGE area,in that case quality is not always guaranteed
IMHO not having a makers mark looks suspicious to me ,I would ask a gunsmith if it's still safe to shoot this gun
