Almost all diesets are designed to resize for the standard jacketed bullet dia. for the caliber. They undersize the expanded case neck (then body on FLS) then the expander ball upsizes the neck ID (on the way out of the die) to give a certain amount of grip around the bullet. This 'works' the brass a lot and shortens case life.
Jacket bullet dia. for your caliber is almost always too small a dia. for cast bullets. Larger dia. expander balls are available to better fit cast bullets.
You can 'neck size' or more properly perhaps, 'partially resize' by backing the FLS die off from the full length position so it only sizes as much of the neck as you need to the base of the bullet you are using. If your load is fairly stiff or more, neck sizing, especially in bottleneck cases, can be problematic. See the recent post about just that.
If neck sizing will work for you, as you can find out with the above method, you may want to consider the Lee Collet Neck Size Die. Many calibers are available and the die alone (rather than the whole set) is available. They are marvelous to get just the right case neck wall tension to grip your projectile of choice, be it jacketed or cast. They also make reloading a snap because there is no case lubing or cleaning same off from sizing.
