A standard FL sizing die sizes the neck down far more than necessary then expands it back to set neck tension via an expander ball. They do this to allow for widely varying neck wall thickness between manufacturers. With many conventional FL dies, if the expander is not perfectly centered, the expander can pull the neck off center. Forster is better than most with this, because the expander is up high on the spindle so the neck is still supported by the die body as the expander enters the neck. They work even better if you have Forster hone the neck of the die so it only sizes the neck down about .005” below loaded diameter. Mighty Armory’s design works well too, because their expander is more of a mandrel and is held perfectly centered within the die by its cone shape. The LCD works well because it only sizes the neck down as far as necessary to get the desired neck tension, so doesn’t overwork the brass. It does this by squeezing the neck around a mandrel. Any inconcentricity is pushed to the outside of of the case, keeping the bullet well centered within the cartridge. Unlike bushing dies, conventional FL dies and the Lee Collet Die size the neck all the way to the shoulder junction. Having tried all of these types of dies, most often, the LCD/ Redding Body die combo produces ammo with the least runout for me.
John