Burch,
Welcome to the board. We have a number of folks knowledgeable about French (and Belgian) guns.
Ideally you can post a photo from your digital camera. Instructions on how to do so are part of the FAQs. The barrel flats and action flats carry information that can help sort out your shotgun. The PT shows the gun uses modern poweder rather than black powder. The 18.2 makes it a 12 gauge shotgun with that barrel (presumably the left) choked, as the cylinder size of a 12 gauge is 18.5mm. The 6.5 is the length of the cartridge in centimeters. Usually given in millimeters, 65 mm is 2-1/2inches. More knowledgeable folks will be along shortly.
Regards, Tim
