I do not do load development with new brass. I do seating depth tests with new brass and primer testing while doing seating tests.
Then, once the brass is fired twice and annealed again, I start load development.
If this is my hunting rig and I have worked up a load and it is proven in stable brass, I then load up NEW brass to hunt with, as I find this to give me the best accuracy and a little less velocity and pressure but stays in the node.
My comp rigs use thrice fired brass that is tight to chamber, then measured with my RCBS Precision Mic and the shoulders are bumped for .0015" clearance then load development is done, including seating depth and powder/primer tests.
Primer testing is a big part of my load development, a primer can make or break a test, so I test them all, BR, Match and standard and magnum, regardless of cartridge. I even test SR brass against LR brass, if available if course.
Cheers.