Learn about shoulder bump with your fI'll length die. All you need is a headspace gauge and some knowledge. Also, anneal your brass every 5 firings or so. I'm sure you'll be satisfied with the # of firings. The accuracy you want to find shouldnt be hard to find. Buy a bullet you want to shoot and a couple powders and work up an ocw test and go shoot.
Like I said before, I would use a twice fired case so you know that it is fully fire formed.
One thing you do know with the info you have, is that the longer of your cases is not longer than your chamber. You could probably just use the .629 measurement.
Using the exact same method you used to measure your once fired case and the same zero on your caliper, measure an unfired case. What is that measurement?
Measure a few and take an average.
pretty much, the shorter ones probably just aren't formed all the way yet. It can take a couple firings to fully fire form your brass.
Did you get that measurement off of an unfired case yet?
That's good news.
Now all you have to do is FL size one of the fired .629 cases and measure that case the same way.