Jimm,
I to shoot the .300 WM in a custom MD.70.I can't guarantee this will help but this is my routine:
1.I use either Norma or Lapua brass (currently Lapua)
2.Check brass for defects
3.weigh brass to +/- one half grain
4.Mic necks to get an average thickness
5.turn necks to within.0002" usually about 70-80%-to make neck wall thickness pretty even leaving it as thick as possible while uniforming.
6.After expansion trim to even length
7.deburr and chamfor necks
8.deburr and uniform flash hole
9.Uniform primer pocket
10.Hope that all of this prep is not a waste of time!!!
I essentially prepair the brass to benchrest standards,because it makes me feel that I have the best possible ammo in the rifle chamber.Then if I shoot a bad group,I can't blame the ammo.
Almost forgot,I check the seated bullet for run-out,not to exceed .0015"to .002",hopefully less.
After posting this,let me say that my smallest 3 shot group was from a Hornady H.M.180gr.factory load:.061".This is what I do in the way of brass prep.I enjoy it.Hope this helps.
Jimmy /ubbthreads/images/graemlins/grin.gif