If it's marked WESLEY- Richards then it's a frawk for sure, as the name is WesTley Richards. However, cased guns are rarely fakes. Pictures are needed - lots of them - showing all the proof marks on and under the barrel.
The Belgians made lots of gun in the latter part of the 19thC and well into the early 20thC that had almost but not quite names - Smeth & Wisson, Horrington and Richardsen, Lancaster and so on.
As Westley Richards are still in business, you can call them up and ask, giving a proper description of the gun, which, from your description, is a percussion gun and therefore prolly dates from around the late 1830s - 1850s.
tac
PS - if its a single barrel, why do you say that it has Damascus barrelS?