So if the hornady 168gn match round chambered easilly and your reloads a TTL, FLS'ed didn't then the tightness may be the projectiles are seated just that bit to long for that chamber the Ogive may be contacting the lede of the rifling I would say bump them back 5 thou and try a dummy one till it chambers easilly and load it to that spec for that rifle.
If the neck was to short then when you cammed the bolt down you'd squish the neck into the projie setting yourself up for some nasty pressures, so I would try a dummy round made to your old spec and go from there rather than chasing out the chamber neck.