G.T. Garwood has an illustration of barrel rivelling in one of his books. The photo was taken after striking off the barrel blue with a sanding block, the absence of blue on the high points clearly indicating the presence of a series of physical prominences or corrugations in the barrel wall. The angle of incidence and reflection of light from a shotgun bore is a very pretty thing and the relative concentricity of the rings has been said to prove a number of things about the barrels (straitness, relative vertical regulation of sxs barrels) but I've never encountered anyone who claimed to identify changes in the molecular architecture of an apparently homogenous material with the naked eye. I doubt if Thomas or Trevallion have either.
jack
