I'd buy a Redding or RCBS bushing die that full length sizes cases with out bending necks with an expander ball. They both use the same bushings and use a bushing whose diameter's 2 thousandths smaller than a loaded round neck diameter. Bushings cost about $12 each so one can get two or three for different neck wall thicknesses their brass has. This is what Sierra Bullets uses to full length size all their cases that such dies are available for in their bullet testing operations.
These dies will size case bodies fired in standard SAAMI dimensioned chambers such that body diameters are reduced no more than 2 or 3 thousandths. That's all that's needed. As the case body's well supported when the neck is sized down just enough so its springback will allow about a thousandths interference to the bullet, case necks will be very straight.
A friend tried his regular RCBS .308 Win. full length die without the expander ball to size cases and found bullets were very hard to seat. That death grip on the bullet caused enough higher pressure to extrude brass at the case head well back into the bolt face cutouts and swell the primer to near 1/4th inch in diameter at the edge of its pocket in the case.
If your chamber's on the big side of specs, you may have to spend more for a custom die made for your chamber so the fired cases aren't sized down too much. Alan Warner's one who makes excellent ones: Warner Tool Company - Reloading Dies
. It's not important that the full length sized case have exactly the same body and shoulder taper as the chamber does. While such things are possible with expensive custom made dies, most of the time they're not needed.
Folks used to just lap out the necks of regular full length sizing dies. I've got six .308 Win. full length RCBS dies with necks at .332" through .337" depending on what brass I use. I don't turn case necks unless they've got more than 1 thousandths spread in thickness.
Redding's web site has quite an article on what causes bullets to have a lot of runout. It boils down to one thing; the case neck has to be aligned well with the case body axis before the bullet's seated.