Dremel a case mouth longitudinally, then size it. Seat a bullet long, measure case head to ogive, with a bullet comparator, write it down, chamber it, extract the dummy round, measure again, write it down. Set the seating stem for a shorter round, but still longer than the "after chambering" measurement. Repeat, until you can load a bullet, chamber it, extract it, and the measurement does not change. Then you will know where your lands are.
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