Your gun was made about 100 years ago by ‘Francois Dumoulin & C°’ (FDC) in Liege, Belgium, one of many artisanal gunmakers in that region at that time.
This type of double barreled pistols was referred to as ‘arme éccosaise’ (sc ottisch gun) although later they became known as ‘pistolet brésilien’ (Brazilian pistol) because Brazil was the main export destination for this kind of gun. The gun was made in a variety of calibers depending on customers wishes.
"Now, now my good man, this is no time to be making enemies."
- Voltaire on his deathbed, in response to a priest who asked him to renounce Satan -