If the extraction was getting harder as the rifle warmed up, it was a good sign that the case hardening of the locking shoulders was finished. If you bring the barrel back a turn, then you have to bring the muzzle end of the fore-end and top handguard back too, unless you slip the block, band, foresight forwards by that amount (a bit of a bodge really...........) Then you've got to re-fit the fore-end at the knox form to bed it again against the shallower taper....................

Get a used but good barrel!