I'd have to ask four questions.

1. What is the runnout midway on the case neck after firing a bullet?

2. What is the runnout midway on the case neck after resizing the case without the expander stem in the die.

3. What is the runnout midway onthe case neck after resizing the case with the expander stem in the die?


4. What does runnout go to after you seat the bullet on the previous measured case neck?

I seriously doubt an undersized expander ball is causing problems. As a matter of fact it should acutally help the problem by reducing friction as you draw the case over it.

What brand of dies are you using? With some of this info it should be easier to get answers to the problem.

kraky,

I probably didn't sound very clear. I was measuring the "roundness" of the expander button/ball itself, rather than the stem assembly. I used a micrometer at 4 points on the expander ball AND a runout gauge with the ball itself on the v-mounts. And you are right, I learned a while back that sometimes the stem can be "adjusted" in the manner you described. Sometimes it helps.

Casey

http://precisionreloading.com/KMProducts.htm

Throw away the expander button..sakofan..Get the Expand Iron from K&M

Well, I am off. This expander ball is not hurting my seating. Took 5 fired brass.

Took out expander ball and ran thru my RCBS:.334" outside neck on all 5. .0008" neck runout

Put expander ball back in and ran all 5:.336" outside neck on all 5. .0015" neck runout

Changed expander ball and repeated on new 5: .336" outside neck on all 5 .0005" runout

Seated bullets:.338" outside neck. So basically the RCBS is only squeezing the neck down .004". I was going to order a Redding S bushing die. but it still squeeses the neck only .001" or .002". Don't think it would help me.

Kraky and Bob, what do ya think?

If you have great runnout after sizing (which you do) but it goes to heck after seating then the problem has to be with the process of seating the bullet. You'll probably never get all of them to seat perfect but should get a high percentage. What works for me is using a low angle case mouth chamferer. I try to make sure I hold the chamferer "in line" as good as possible with the case mouth while deburring. When seating I just start the bullet into the case mouth then rotate the case 1/2 turn and push the bullet in further, then another rotation of the case and finish the push into the case. Some people think by working the bullet into the case and then changing the position and working it more it will go in straighter and it's worked for me. I just don't know what else to tell you except if your case mouth is very straight and in line with the rest of the case you should not grow runnout by more than a thousandth or two during the seating process. I wish I could be there with you when you seat the bullets to see if the "feel" is the same as I get.