Its impossible to measure the shoulder of a bottleneck cartridge with calipers. You need a case gage.
Most likely you havent set the shoulder back far enough for the bolt gun. Ar15 typically have pretty loose chambers. Bolt guns tend to be chambered at or very close to saami minimum.
If your raising your shell plate up to top screwing the die down till it hits the plate method of sizer die adjustment, thats just the starting spot and is generally too long. You need a case gage to get the correct saami case measurement set.
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