A Google search of A513 steel yields the info that it can be anything from 1010 to 1020 (tensile strength of 45Kpsi to 52Kpsi) which is the mild steel range. Most of us are satisfied that mild steel (1018 CR or 1020 HR) is suitable for making muzzle loading black powder artillery provided reasonable design is used. It does have the endearing quality of welding easily and well.
However, all DOM tubing I have seen described by its manufacturers has been called things like "electrical resistance welded tubing" which means it is NOT seamless.
