I know this is an old thread, but we didn't answer JDW's last question. It doesn't matter what the bore diameter is, you use the .700 ring on the Skeet's or Galazan micrometer to zero your micrometer and determine the bore and choke of your 16 or 12 gauge based on the .700 base figure. Again, the difference between the bore and the choke at the muzzle is the choke dimension. When you are buying an expensive gun and originality is your goal, you have to know what "original" is and what your prospective purchase measures. Rookhawk will pay for his gauges on his first purchase. He has bought the right tools without paying an exorbitant price.