You have to re-size every case either full length or a neck size. With full length you get less brass life say 10-15 times through & need lub & i advise you trim/chamfer & pocket primmer clean every time. Neck sizing as said only dose the neck & no need for lub & cases last 10 times longer but this method of sizing is more for target/benchrest. You need to size every case as the case mouth expands when fired & needs to be taken back 0.001" smaller than the bullet. the expander pin in your die will do this job so dont get anal over it & you should get better accuracy