If you are going to experiment with different seating depths, ALWAYS start with a below maximum load and start with the seating depth closest to the lands of the rifling. Succeeding test loads should then have the bullet seated deeper (i.e. - shorter OAL). Once you have found the optimum seating depth, then you can experiment with increased powder charges. As BrentM said, pressure will increase the closer you seat the bullet to the lands.
