Is it more likely that sizing dies would pull the neck crooked or that my chamber in the rifle is lopsided?

Tried 2 seaters and several different bullets and the seater is not the issue. Only brass fired in this rifle is affected.

Huge runout on these reloads.

What kind of dies are you using? You should try shooting some factory ammo and see what the brass looks like after firing. Some guys say that the expander pulls the neck out, thus affecting concentricity, but I've never seen it with my dies or reloaded ammo and I religiously check loaded rounds from new dies every time. With run of the mill RCBS dies, I get .003" or less run-out. It could be your chamber, especially if it is a WSM with a skinny barrel. Some of the early winchester WSM's were known for having egg shaped chambers.

Easy enough to find out. Check runout on the fired brass before and after sizing and compare.

This is a remington 700 .243.

I don't have tooling to check run out but I do roll the finished cartridges on my bench and this showed huge wobbling.

I seated a bullet in brass that was not sized or fired in this rifle and the wobbling was not present.

So it could be the sizer or the rifle. I am leaning toward the rifle as I have never seen this happen due to sizing.

This was factory ammo which was sized and loaded after firing once in this rifle.

Hard to tell without a runout gauge..

It's more likely that your expander ball is pulling the necks out of alignment than that your chamber is out of round. Try sizing without the expander ball in place, and see if the cases are still crooked. Some dies have been cut with crooked necks, as well. If the cases size straight with the expander ball removed, try running it into the cases from the top, on the press handle downstroke, rather than on the upstroke, with the ball inside the case when it is forced in the neck. I've all but stopped running the expander ball into unsized brass from the shoulder to the mouth of the case. If I have to run an expander ball, I run it from the mouth to the shoulder, then back out.

If none of this makes a difference, look at your fired brass. If it's crooked, it should be obvious. I've seen some weird cut chambers, but nothing out of round.

I had a Bergara encore barrel with an egg shaped chamber so I know it can happen...but i will try running newer brass thru this die and see if that's the issue

Step 1: Get a runout gauge.

Step 2: Switch to Forster dies.

Step 3: Load ammo with new dies.

Step 4: Confirm runout is gone.

Step 5: Go shoot small groups.

Betting this is a rifle problem as I have used 2 sets of dies now with the same issue

This^^

A concentricity gauge will tell you about a fired case (chamber), a sized case (sizing die), a loaded round (seater).

Rolling a loaded round across a flat surface a guy can often see bullet runout, but it’s a lot more difficult to see neck runout rolling an empty case.

You said you switched dies but did you switch shellholders? Could be your shellholder is bad and tweaking the brass when you pull the expander ball out of a sized case. Also what kind of press are you running?
I have to say I always heard about runout problems and kept putting my reloads on a mirror and rolling them and could never detect any runout. Then I got a concentricity gauge. Guess what? My RCBS equipment was giving me loads that consistently measured .001 runout or less.
I did have 1 necksizer that induced about .007 runout that RCBS gladly replaced with a FL sizer but another shocker- the groups with that rifle
improved only slightly. So IME runout is like primer pocket uniforming, it might help the BR guys but for 99% of hunting, it is mostly a waste of time.
That being said, I check my loads just to verify that something hasn't gone wonky in my process but the concentricity gunge mostly just gathers dust.

Good thoughts, thank you. I use a lee press I have had a long time. Never had this issue before now.

MJB,

Concentricity Gauge I use. It's answered a lot of questions for me.

https://www.midwayusa.com/product/1012691754?pid=292524

It's a good time to invest in one. With the current component shortage, it's best not to be wasting any.

A good point

Annealed? or not?

Conceptually, if a neck springs back from resizing, can the expander ball exert enough pressure to cause misalignment of the neck?

Have you loaded fresh brass and they come out wobbly ? That points to your dies.

Just tried brass not from this rifle. Straight and no problem. Guess I need to locate a new barrel