I use one that has two 5/8" rods and another with a 1/2" rod. It is like the Galazan one but homemade. I can measure half of a 32" barrel then turn it upside down and measure the rest. My first reading is 4" and I turn the barrel from top rib to bottom rib and record the lowest reading. Move it up 2" and do it again until I have to turn it around and do the same. I only record the lowest reading and mark that in my records.
It does take some time to do but it worth it.
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