Well done again Mr Horton. And a good bit of info from smellie as well.
No matter what you may read elsewhere that is given as gospel- there is no such thing as a chamber that was machined not concentric to the barrel bore. Perpetrators of this myth have misread the results of shooting undersize brass in the "generous" Lee Enfield chamber and sometimes with a missmatched bolt that didn't bear evenly on the locking lugs. The marks on cases they are reporting have very little to nothing to do with headspace either.