Bobby and Aaron make good points, you'll not likely get great accuracy neck sizing, there's too much action flex in the Handi frame to allow it to work well with anything above mid level loads with high pressure chamberings like the 30-06 family of cartridges, if you can't chamber the brass so you can place a straight edge level across the barrel face, then the brass needs to be full length sized, if it isn't level, the action may not lock up completely and you'll get poor accuracy and maybe even pop opens. I size my brass just enough so it's flush with the barrel face using a straight edge, not just visual, if the straight edge has any rock to it, the shoulder needs to be pushed back a little more.
Tim