Well, I'm sure JB likes his tubing but the facts are that the only truly seamless tubing is too expensive and difficult to get for making barrels.
The "seamless" tubing used by some is actually welded tubing which has been run thru dies to smooth out the weld joint. This is often called "DOM" tubing which simply put means "Drawn Over Mandrel".
Doing this allows the tubing to be used with the various fittings that require an accurate, very smooth exterior.
While some DOM tubing is available in some high strength materials that may work for a gun barrel the vast majority of the DOM tubing is low carbon, low strength material that is totally unsuited for use as a gun barrel.
Any gun barrel from Colerain, Getz, Rice, Green Mountain, Orion, Douglas, Numrich etc is made from wrought material, not DOM tubing.