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Originally Posted by Bart B.
A 308 Win perfectly straight cartridge is slightly crooked in the chamber when fired; for each .001" off center the case head is, the bullet tip is almost .001" off center in the bore.
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Yes, but it needs to be pointed out that mislocation tends to be consistent shot to shot. Both A. A. Abattielo's old test of 42 lots of 30-06 NM ammo measured for runout and Harold Vaughn's tests showed that if the off-axis error is located in the same place for every shot, the error sends the bullets to the same spot.
Have you looked at how far off the pressure ring is in a resized case? I don't expect perfect roundness from resizing but haven't checked that particular value myself.
If you could assume perfect case body symmetry, this is how measuring the supports (small circles) in different locations would measure the same cartridge:
