A number of Belgian makers produced these Flobert rifles. The one pictured looks to be a step up from the run of the mill with its engraving, double set triggers, and provision for a tang sight. The trapdoor breech is of the Warnant system. There should be Belgian proofs and makers marks on the barrel.
The time frame can be narrowed down somewhat by the marks, however general era would be circa 1880-1914.
im not gonna lie, that trigger lock is the best ive ever seen on a gun before!