How do you telll a damascus shoyun barrel?

You will notice many small lines,circular lines through the steel. Damascus is actually laminated steel which could accept the much lighter pressure made by black powder shot shells.

If the fine lines are visible in an area where the steel is lightly worn, then the barrel is likely damascus. If the lines are not visible, it is possibly "fluid" steel, meaning that it's not damascus. Up until early in the 20th century, gun manufacturers attempted to duplicate the appearance of damascus on what were stronger barrels.

In either case, do not shoot the gun until you have had a gunsmith check it out.