Grizzley1 is right, but I think this gun is older and dates back to the first half of the XIXe century.
. For sure, it's a Belgian shotgun from Liège (ELG stamp, but I cannot count the number of branchs of the star)
The barrels have the "provisionnal proof" ,E and L in english letters (near the 16,6 marking referring to the diametre in mm). The "perron" (the Column, representing a monument in Liege) is the proof for the mechanism. The letter with a star on it is the controller.
The diametre being 16,6 millimeters, it is a 16 gauge (16,8mm) with a choke.
JM could be Joseph Monisse but this does not really match with the time frame of production of this shotgun, as he was active much later in the century
I think this marks are the ones of sub contractors.
The style of engraving is familiar so I will search a little bit more.