First, I question whether that's a duelling pistol. Traditional duellers don't have sights and usually have bronze barrels. It looks to me more like one of a pair of horseman's pistols. I'd suggest they were made circa 1800, and I'd be really careful about trying to cock it. The hammer looks like it's been cracked and brazed in the close-up photo.
If the plate on the right side is correct, it was made in Munich. You might want to have a German-speaker take a look at it.