so you start going over book max. charge 1,2 ,3 grs. when do you accept you have a slow rifle or maybe ultra smooth (slick) barrel or other reason to not build the pressure to reach target velocity to where you need more powder to reach pressure ?
When you get "pressure signs" ! !
Seriously I don't have definitive answer to your ? That's a problem I've never encountered BUT I know that others have.
Mr. Denton ? Mr. Mule Deer ? et.al.
Jerry