When I lived in Colorado several years ago, I met an older gentleman at an elk camp that was a well respected gun builder. At the time, I was not very experienced(not that I am now either) and I asked alot of questions. When sizing came up he had his own opinion. Building mostly belted magnums, he stated that bumping the shoulder led to greater work hardening of the brass and higher incidences of split case necks, case wall stress and case head separation. He sized his competition ammo and hunting loads this way with fireformed cases. Screw the die down to the shell holder and back off 1/4 turn or so and size the case. Chamber it in the rifle and begin to close the bolt. Bolt will be tight and considerable cam force would be needed to go into battery. Incrementally adjust the die, size and chamber until the resistance is felt in the last third of the bolt closing. His opinion and experience was that this gave the most concentricity with the least force and would extend case life. He said he would neck size only if it weren't for the lack of dependability in adverse field conditions. If I've been drinking the Kool aid, it must be spiked pretty good because it's worked well for me. It's more time consuming but the benefits have been evident in tighter groups at long range and full freezers