I have found that if the expander ball is removed altogether the necks come out of the sizing die straighter. There are 4 routes I have found to work well.
1) Custom FL sizing die. Forster will cut the neck of their sizing die to fit your case. C&H Tool and Die will make one for you if you provide 3 empties fired in your rifle.
2) Bushing FL sizing die. I prefer the Whidden made ones.
3) Redding body die followed by Lee Collet die.
4) Standard sizing die without expander ball followed by a Lyman "M" die or a tapered expander plug as one would use when neck turning.
Somehow it seems that if the axis of force used to expand the neck is on the down stroke of your ram versus the upstroke of the ram, one is more likely to get higher runouts on his case necks. I don't know why that is.
Of course this assumes many things, including cases of uniform brass thickness all around. The guy who made the NECO case gage tool wrote an article (it may still be available on the NECO website) in which he described the "banana" case phenomenon, where the case wall is of non uniform thickness, at the moment of firing will bend towards the thickest portion, thus tilting the case neck somewhat in the bore, the end result of which is the same as cases with higher runout: the bullet is released into the bore with the point off center. I also remember that he experimented some and found that if you measured the case wall thickness, and inserted the cartridges with the thick side down each time, that you could get extremely good accuracy from non concentric ammo. --I'm paraphrasing here, but I do remember that he said that a banana case indexed in the chamber the same each time gave him better accuracy than cases with little runout.
