Begin with bullet weight and make in mind. Search data for likely powder. Test single cartridges for range of loads per powder -- check pressures. Load five or so of each weight group (powder charge) and shoot groups for accuracy. Vary OAL for powder charge(s) selected and see if any gain in accuracy. Chrony resulting loads to compare with published data results.
I do something like this, but those 5 or so rounds I load to test pressure will go over the Magnetospeed. If I find the velocity window I want within reasonable pressure, I will usually go one of two ways: If getting near the land is not possible, I'll pick a reasonable OAL and play with charge weights, loading a few 4 round test batches for accuracy. If getting near the land is possible, I'll stick with one powder charge and experiment with 4 round batches at varying OAL. I'll try to shoot at 200yds on days without much wind. If I can get reasonable groups (depending on expectations for the rifle), I'll load more and shoot at 300/400 another day.
