Damascus Twist Barrels - Barrel tubes built up by twisting alternate strips of iron and steel around a fixed rod (mandrel) and welding them together in varying combinations according to the intended quality and the skill of the maker. The rod was withdrawn, the interior reamed and the exterior filed until the finished tube was achieved. Damascus barrels may be recognized by any of a variety of twist or spiral patterns visible in the surface of the steel. Before the 20th century, barrels were typically built in this manner because gunmakers did not have the technology to drill a deep hole the full length of a bar of steel without coming out the side.
Damascus barrels were usually intended for use with black powder---the standard of the day. The contour of the barrel wall thickness, intended for the fast explosion of black powder, was quite thick at the breech and tapered thinner towards the muzzle. It is not advisable to shoot modern smokeless powder in a damascus barrel. Apart from giving due deference to the age of such barrels and to the method of their construction, smokeless powder burns more slowly, lowering the pressure at the breech end, but considerably raising it further down the barrel to a level such barrels were rarely designed to handle