Trying to minimize runout during neck turning process

[Allen1]

My process for turning necks has been to FL size them with a standard die with expander ball to size the necks all the way to the shoulder and using a expander mandrel to give the right fit for the pilot on the turner.
I know there has to be run out introduced during this process. I'm not able to correct the runout in the neck with a bushing die because it is sized down to far.
Would getting a separate mandrel about .003-.004" larger and expanding the necks to where they can be re-sized in a bushing die be of any benefit?

 

[BoydAllen]

In my experience, because the bushings generally float, bushing dies don't straighten very much if at all. On the other hand, if you eliminate the expander ball in the one piece die, and use the mandrel exclusively, I think that your concentricity will improve.

 

[bugman]

+1 on eliminating the expander ball in the FL sizer....and plenty of lube on the expander mandrel will also help.

 

[mikecr]

I expand NEW brass with a Sinclair expander & neck turn. With this, getting the right fit on turning mandrel is not an issue.
I've never tried turning fired or sized brass, and I don't see a good way to do it as well.

 

[Allen1]

Why does a mandrel produce less runout than an expander ball?
The case isn't supported. It's just a different direction as best I can tell.

 

[BoydAllen]

It would only be a guess as to why, but there is no doubt that it works that way. I have tried it both ways and measured the runout. I used a one piece Fl die to size fired, un-turned .22-250 brass. I had to work with what I had in front of me. Before I processed the whole lot, I tried several cases both ways and measured the runout. The difference was significant. The insides of the cases' necks were lubed.

 

[FeMan]

I have found the same thing; buttons are very bad for concentricity. I have my best results FL resizing with no bushing, then resizing necks no more than 5-thousandths at a time. I oversize slightly and then use a lubed Sinclair mandrel. Most of my cases are dead nuts.