The producers of this series can't make up their minds of the time period of the series, particularly as it comes to hand guns. Filinta's gun is definitely a modern type revolver which came into existence towards the latter half of the 19th century however at times it is referred to as a flintlock even though it is seen in the opening credits firing a modern type copper jacket bullet. Other characters use flintlock firearms which were definitely obsolete by the time period of the series. Some characters used cap and ball revolvers which were prevalent from the 1830s till around 1870. They used black powder and percussion caps to fire the weapon. All of these types of weapons can sometimes be seen in the same episode.
Filinta's revolver as shown in the opening credits and used in the series, would not be able to work as powerfully as is shown. There is a gap of at least 1/8" between the front of the cylinder and the breach of the barrel. The gases used to propel the bullet through the barrel would nearly all go out through the sides after it left the cylinder leaving very little power to get the bullet out of the barrel.