and thats how a lot of ppl do it but it dont work so well for me...i will set my LOP to where the butt is in my shoulder but not real firm i will then shoot a few rounds and if i feel myself wanting to roll my shoulder forward i will lengthen the LOP...this allows me to move forward or back without having the butt to tight or to loose...for me if the butt is in my shoulder to tight i have a hard time staying still on target if the butt isnt tight enough i catch myself wanting to roll my shoulder forward.