Yes, seems very light indeed for a 16. I'm pretty sure it's a rho as it's kind of elongated and both are identical.

There is the "16.9 choke 16.8" on the barrels which I'm assuming are the bore and choke measurements in MM.

It has the Anson release on the forearm which I hadn't mentioned.

Seems probable to me that it was a special order for a local distributor in Coulommiers and named "Briard". possibly from Nicolas Lajot if that group was still in business then.