Powder J was used between 1896-1914. After 1914, the only smokeless powder used in proof loads--and still in use today--was Powder T. (Same mark as on this gun, but PT.) So the gun could not be any older than 1896, which is somewhat odd because the proofmark on the barrels with the E was supposedly gone, either by 1879 or 1886. Maybe the St. Etienne proofhouse was running a special on leftover proofmarks.
But seriously, I'd go with the PJ mark and date your gun somewhere in the 1896-1914 time frame.
