I know for a fact that my modified case for 6.5 Creedmoor is NOT the same distance from base to datum point on the shoulder as my Go Gauge. I've measured both. Measure the difference between the modified case and your sized case and add the difference. I use a fireformed case myself. If you are bumping the shoulder back.002 then I think it will work either way. Some bullets vary .002 or more in base to ogive. I don't think 2 thousandths is going to make much difference unless they are jammed.