"This is almost always in a 3-4" area very close to the top rib or bottom rib, and only on one side of the tube. As one person on this thread mentioned, virtually all vintage American doubles have a very noticeable lack of concentricity, ie thicker on one side than the other. There is also the matter of soldering on the ribs, with the required filing of overflow solder tight in to the rib, creating these thin spots."
Jay,
Thanks for the above reply. On almost every set of barrels, this is where I do find the thinnest spots. I had never understood why as one would think this area would not have been the one to meet the file as much as the outermost metal. The tendency is to measure the outside three-fourths of the barrel away from the ribs for thickness and to ignore the one remaining fourth of the barrels for measurement next to the ribs. Now I know why that is where they are the thinnest there. I see it on top more than on the bottom, with lots of low .020 measurements on smaller framed guns.
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