I only use a bushing die for a .308, and set it up as follows:
1. Measure the neck O.D. of a loaded round with the brass you are sizing.
2. Subtract the amount of neck tension desired from the measurement above. I use .002 for single loading but you may want more for magazine feeding. This is the bushing ID to use.
If your fired case neck O.D, is much larger than the desired final neck O.D. you may need to size down in steps with two bushings to reduce run out. I use a lee collet die to start the sizing and deprime, then tumble and set the shoulder back .0015 with the bushing die doing the final neck down.. With uniform brass like Lapua, you can get by without neck turning or the expander on the decapping rod.
I just spot check 10 loaded rounds from the dies that have now loaded 4000 rounds since set up and the worst run out was .001" measured on the ogive.
I'm sure there are many other ways to do this, but this has worked well for me. BSA may be along shortly to tell us we should not be using bushing dies... grin.
