The ERW (Electric Resistance Welded) tubing is very useful for the
construction of receivers and magazine, or as sleeving to reinforce or
increase the diameter of another tube. It should not be used as gun
barrelling - unless nothing else is available - due to its welded-seam
construction. The SMT (Seemless Mechanical Tube) is ideal for improvised
gun barrels. Because of the many different tube sizes available, it is
possible to construct a barrel to suit almost any calibre of firearm.
Where possible, heavy-gauge tube should be used for barrel or a lighter
gauge suitably reinforced with a second tube or steel collars. While
many tubes will be of perfectly adequate strength on their own, it is
only common sense to make the tube as strong as possible, providing the
design of the gun will allow it.