I started using a resized case,seating the bullet,then pulling the bullet with my collet puller,then seating it again long.Then I slowly chamber the case with the bullet and close the bolt.After the bullet has been pulled and reseated,once it hits the lands,the bullet will slide back into the case when you close the bolt.The case will hold the bullet tight enough that you cannot move it by hand,but loose enough that the bullet can move when chambered.I save that dummy case as a reference to know that is my absolute max length to lands.Then I know to seat down from that.