The problem is that MT or PT would not only find your flaw but would find the surface welds of a Damascus barrel. MT uses a ferrous powder and then it is wiped off. The powder stays in the crack and is visable upon magnetization. PT uses a red dye that seaks cracks. The red die is then removed from the surface but stays in the crack. A white developer is then sprayed onto the surface and the red in the crack shows. Radiography (RT) might show the crack if is was much larger than the welds in the barrel but with a defect that big, you would not need any form of NDE to find it. -Dick