Even though the material may be pattern welded, a barrel seems to be intended to act as a uniform material. Maybe the lab folks could evaluate the tube without concern for the material, but as mentioned things get complicated when they're arranged as a s x s gun barrel.
Earlier discussion about formulas to estimate pressure vessel burst performance made me wonder. If(?) static pressure can be used as one type of measurable performance, maybe adjustable resilient plugs could seal a tube for hydraulic pressurizing. Could be easily controllable for an anticipated tube wall thickness and should show leaks, but maybe not relevant.
