Thanks for answering.
I feel like I bought a BP rifle instead of a Nitro!
The only mark on the barrels flats is 450 Ex. I have some good pictures but I can't find the way to post them on the forum (anybody can help?).
The rifle is almost new, perfectly on face, with gorgerous woods. It has 26 inches barrels, full rib with one standing and one folding leaves, splinter forend.Serial number is 13082. Weight 9 pounds.
I bought it used from a gunsmith in Paris with 60 cartridges (A Square) .450 NE.
I tried these and accuracy was very good at 70 yards. But primers were too flat for my tast!
Do you think a BP rifle would have stand such loads?

I would be very pleased to share pictures with fellow DR lovers!

Chris