FWIW I use a stoney and get an average after about 10 readings. I take that and regardless of if its correct or not I use it to decide my depth. IE subtract or add XY amount to that figure and start testing.

Then I end up with whatever is most accurate and make a dummy round of that with a bullet. You can bet your throat will get longer and not shorter so when accuracy dives a bit, I"ll go back to the dummy round and add a bit to OAL.

Its not scientific, but it prevents me from wondering which figure is right etc..... But then again it probably works best for me since in my match ammo I tend to jam the bullets almost all the time so I simple add to the figure and am happy.

Jeff