I use a Hornady concentricity gauge to check rollout on my loaded rounds. What I have found while using this tool is the brass makes a huge difference when searching for consistent accuracy. I have not been happy with the brass I've purchased for my Winchester 264 magnum.
Last November I took possession of my father's 1965 Win Mod 70. I had no load data from him or ammo. I bought a box of Super X and first thing I did was roll them on the concentricity gauge. Wow, .022 of crooked mess! So I did an experiment. Kept 5 at factory loaded mess, 5 I straightened with the gauge. The other 10 I straightened the round then pulled the bullets, dumped the powder and averaged the charge and resized the brass. I noticed when you straighten the round with the gauge, it will reduce neck tension if you have to really push on it to get where you want it. So the next 10 rounds will focus on neck tension. I loaded up 5, same powder charge, brass as good as my FL resized could do, and seated the bullets to the same depth. The last 5, I measured the brass at 3 points, mid body, shoulder and neck. I seated a bullet deep (no powder or primer) and eventually straighten the brass at these 3 points. The bullet may not wobble at the ogive on some rounds but I noticed the body of the brass was. So, the last 5 were straight from bullet tip to half way up the body. I pulled the bullet, resized the brass and loaded. There was a noticeable difference in accuracy between all of the groups. One thing I learned was when I use the gauge to straighten a round, I push on the neck just above the shoulder neck junction, or base of the neck. This has far less affect on neck tension. If the brass is really out of wack, I also push at the shoulder, being careful not to dent the brass, Just a few thousandths here then finish at the base of the neck.
So to recap, a straight round (consistent powder charge, seating depth) shoots pretty good unless the neck tension is all over the place. Now for neck tension, next post