Ouch!
If I was going to load new cases and then fire them I would fire them and then eject once fired cases. But if I had any grand plan on the result I would measure the length of the new cases from the shoulder/datum to the case head first. I would load and then fire them and measure the length of the fired cases from the shoulder/datum to the case head again and then compare. I would not claim I measured, I would publish the measurements; The OP claimed he moved the shoulder back .002". I understand everyone reading on this forum assumes the chamber is .002" longer than a minimum length/full length sized case and the sized cases is the same length as the new cases from the shoulder to the case head.
If that were true it is safe to say he has a short chamber and I always wonder why no one ever aske a reloader how he manages to move the shoulder back .002". I can shorten a case from the shoulder to the case head .002", I have never managed to move the shoulder back.
And then there is that thing with 40 fps spread. I will have to assume he shot the new cases with 'O' spread and then sized the fired cases an got a spread of 40 fps.
Back to ouch: My fire forming load became the maximum load for a 200 grain bullet after the case was formed to the chamber. And Hodgdon said it could be over max. I formed those cases once. The only problem? was during the forming and fire forming process the case shortened .045" from the end of the neck to the case head.
And then there was something else no one would notice: The firing pin did not drive the shoulder forward to the shoulder of the chamber.
F. Guffey