C'mon Boom, it ain't that mysterious. Of course a little fine tuning may be required but there are "reference loads" that take a lot of initial guesswork out of the situation.
For example, if a guy came to me about 308 loads and he told me he had 168 grain bullets and some Varget I could send him away with a lot better guidance than "go experiment" because chances are his 308 isn't going to be radically different from the other hordes of them that shoot lights out with 46 grains.
