Looks French to me. The word Acier that is stamped on the barrel means steel in French. The very first shotgun I ever bought was French and had Acier Special stamped on the barrel. I still have it. For years I thought is was a boxlock but upon further inspection found it had a lock plate mechaniism, At first glance, that gun appears to have quite a bit of drop on the stock.
Has 65mm chambers, too. The chokes will be real tight in a gun of the 65mm chamber vintage. It's been opened up underneath by someone who didn't know doubles. Still, it's a nice field grade SXS.