There are stories about tubing with flaws, solid bar stock with flaws, drilled bar stock with flaws, extruded stock with flaws, testing methods with flaws, high strength alloys with flaws, hand welded wrought iron barrel flaws (wrought iron is often mostly flaws loosely surrounded by some iron)...$#*!, I think even the flaws have flaws.
ANY material can have defects and ANY manufacturing method can produce discrepant parts. In the aerospace world, we pay to have materials for critical components 100% inspected (NDT..."Non Destructive Testing" like X-ray, Computed tomography, magnaflux, etc., is applied to ALL the material and ALL the finished parts) .....and then we proof test the finished part anyway. IMHO, you can make a safe barrel out of all sorts of materials if sufficient inspection is applied to the starting material you are working with and then, as is always prudent, proof test the finished product.
If you want an absolute, iron clad, 100% guarantee that a gun barrel will never fail on you, don't load it or shoot it.