Interesting. Lefaucheux was at this address (10, rue de la bourse) between 1834 & 1835, and between 1845 and 1850, when he moved to 37, rue Vivienne, on the next block. Unbelievably enough there is still a gun-shop at 37, rue Vivienne.
The action of stocking is called "monte a bois". "monte" can be used for some of the assembly or finishing. The French language is a bit surprising from a Prague worker, but French was the lingua franca of Europe at the time. The inscription means "finished by the the nephew of Kehlner in Prague". Probably the nephew successor of Anton Kehlner who died in 1841 in Prague.
I don't know what's behind the duck on the breech, except maybe it was the intended target for the gun.
Amazing barrel work...