Tinker, Here's how I would proceed with a rifle previously regulated with an unknown load. Use standard loading tricks to bring regulation as close as possible. A chronograph is very handy to stay in the ball park regarding pressures and velocities. When you have a load that groups well but is 6 MOA side to side, up or down, or crossing, the crown can be used to move the groups as necessary. If you have a mill available, you can fix an over zealous grind on the crown by simply milling off a bit of the muzzles to get rid of all crown and start over. Better if you go slowly and shoot a lot. Trial and error still has it's place!

Otto