While it is true bbls have been made by rolling a flat bar & welding with a loingitudinal seam, it is equally true bbls have been formed by "Rolling" a short fat cylinder into a long thin one. This may well be the method used to make these bbls. With this method the bbls were I believe normally rolled while at a red heat, over a mandrel with outside rollers to give the shape, unlike the modern cold forming methods of hammer forged bbls. The strength of a bbl made by this process would be dependant primarily upon the alloy of steel used, most likely a very mild alloy.
