I see that 'crack' as a success in this way. It is with the grain that was formed by the steel drawing process. By grain, I mean that the dark pools, inclusions, have been decreased in size, surrounded by sound steel that is directional.
While there may be switch backs with twisting and hammer strikes, the continuous direction of the rods are formed on a mandrel roughly opposing the direction of the barrel tube. In other words, they're arranged to form hoop strength. I'm not thinking a barrel can't fail, only that there may have been an engineering intention to the construction back at a time when the mills couldn't assure consistency.
Just conversational opinion Doc Drew, to me your various images are much more interesting than often held assumptions that damascus would look like a mess of welds. Could the straight lines be abrasive scratch patterns, either not fully removed during the sample prep or as a result of the sample prep. Slight warpage and material hardness variations could account for seeing a scratch pattern in one area and not the adjacent?
