Concentricity, the lee dies do the job..... But if you want to have accurate bullets you gotta have the tolerances within the dies....
runout is expeced to double once you seat the bullet, with good quality dies, tolerances are that bit tighter,
now i had lee dies, And got good accuracy, but after runout was checked on a concentricity gauge of neck runout, i seated both bullets one with the lee and one with redding,
the runout slightly more than doubled with redding and was .007 to .009 with the lee,
anything below .04 is classed as good.....
you get what you pay for,