What is described here is "partial full-length resizing, it is NOT JUST sizing the neck, as any partof the die that touches the case is going to size it somewhat. The straighter the case, the more this happens.

To neck-size only, you must have a neck-sizing die. However, I use an FL die, and adjust it to only resize about the first 1/3 of the neck, just enough to firmly grip the bullet! The actual amount of required neck sizing varies somewhat from cartridge to cartridge, but works out to be about 1/3 of the neck. Even set this way, there is still a little sizing of other parts of the case, but the shoulder is left where it should be. One must use some kind of lube (Motor Mica or powdered graphite) inside the caseneck to keep the expander ballfrom pulling the shoulder forward, when sizing cases that have this tendency-not all calibers do. Neither do carbide expander buttons.