Would go with 3rd quarter of 19th century. It's a Colt Navy knock-off, if you will, hence the name "Brevet". Could be Liege made and Montenegran proofed...don't find any real source of gun manufacture at that time or later in Montenegro. Everything they used then and later was usually Austrian, later Russian. The revolver is a curiosity but should be enjoyed. Cylinder seems long for the frame, the hammer does turn rather upward and the cylinder surface may or may not have some sort of tantalizing markings, engravings or Lord knows what. Don't really know what to make of it but golly, is it ever interesting. I would suggest you attempt to get some more detailed photos of it from the sellers, which may or may not even be possible. It's got it's own character but don't mortgage the farm for it, it'll never be worth any sort of big dollars.