Skelp (sometimes spelled scelp) is wrought iron or steel that is rolled or forged into narrow strips and ready to be made into pipe or tubing by being bent (into a cylindrical shape) and welded.
Cheap gun barrels could be made this way in the Damascus method—wrapping the skelp around a mandrel to make spirals which were then hammered and forged into a tube.
The mandrel was then removed, the interior reamed, and the exterior filed until a finished tube was complete.
This method of fabrication was used because it was difficult to cast a solid barrel and then drill it out without the bit coming out the side.
In such contexts, advanced smithing and filing skills have often made up for the lack of machine tools.