What is the procedure for finding BOSS sweet spots when using a bullet weight for which no setting is provided?
Check the sweet spot chart for the closest comparable load and setting as a starting point. If the velocity of your new load is greater, then the numerical value of the BOSS setting will be higher. If the velocity of your new load is lower, then the numerical value of the BOSS setting will be lower.
If you desire to further experiment and possibly obtain even tighter groupings, turn the micro-adjustable lock nut 1/4 of a turn clockwise and fire your rifle at a safe target. If the group opens up (gets larger), turn the micro-adjustable lock nut counter clockwise and sight in at different 1/4 turns until you are satisfied with your groupings.