Check your base to Datum again after neck sizing. Neck sizing seperately will change the Datum, draws in the angle, so include that in the end results. Sinclair expander will work, check to make sure it is true and centered in the body for it, some are not, lube it, Imperial. Case neck's square and inside chamfer square. Graphite powder the neck's. Straight bullet placement before seating. Check shell holders for square, some are not.

Just some tips, Brad