12brd - nice to have a definitive answer, and thanks for sharing.
It would be informative to know the wall thicknesses at the burst, and which trap load, if you could please ask the owner. Pressures at that point are probably < 1000 psi

1 1/8 oz at 1200 fps



That is called "brittle cleavage" (which does NOT mean the metal is brittle) in that there is little plastic deformation. A damascus barrel with a much lower yield strength will "stretch" before bursting, if the wall does not fracture along a weld.

Part of this burst appears to be along the ribband edge weld


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