A few preliminary thoughts. I've searched "Marquis de Courier" (I believe from the blurry rib this is the spelling) on French web-sites and nothing comes up so far.

[Linked Image from i.imgur.com]

Blvd des Italiens was a prestigious Paris address. I suspect Courier was an "Armurier" - a gun merchant; Armurier's all over France sometimes assembled guns using parts from Paris or Saint-Etienne and put their names on them if they had enough prestigous clientel.

SNC? needs clarification. Normally "SN" will be "Société nationale". Might this be SNCF, i.e the French national railroad - Société nationale des chemins de fer français?

I suspect also that the gun (or at least the barrels) was made by legendary Parisian barrel and gun-maker Leopold Bernard, the gold standard of French barrel makers in the 19th century. Bernard always dated his barrels...there should be a date on there somewhere. At least by 1881 some claim he was sometimes using Belgian barrels blanks.

The barrels look to be stub-twist Damascus. (Even as early as the 1860's France and Belgium far outstripped UK in the decorative patterns of their Damascus. Stub-twist remained the UK normal up to about 1865. So it's a little surprising to find this pattern on a presumably 1880's gun. Dr. Hause can comment further). Standard French barrel length by the late 1890's was 27.5". The fact that these are 29.5" makes me think this is an earlier gun. Side-levers are rare in French guns.

The chamber length should be on the barrels. by the 1890's at least most Saint-Etienne guns were chambered for 65mm (or 6.5 in Saint-Etienne only)..i.e. 2 1/2". But there are a lot of guns in the 1880's that had longer chambers. It will be black-powder proofed unless reproofed.

The Barrel bore should also be stamped on the barrels in mm.

We need pics of the proofs and all the marks. I don't know Parisian proof-house stamps as well as Saint-Etienne but photos of the proof marks and other markings on the gun would be a good place to start. Get a free account on imgur.com. You can then download the photos and post the code here.

If Leopold Bernard made the barrels, you have a blue chip. Will look into this further tomorrow. But that sir is a very attractive gun!

Gene Williams