zeke: "Not all presses are the same. My Rockchucker does not have a floating die holder, or allow a locked down die to float (square up), so i float it before locking it up."
on presses like the RC the float the shellholder allows is sufficient to allow the case to align itself to the dies.
Back to my OP. I believe neck misalignment occurs when the case is being withdrawn from the die and the neck is not supported by the die walls. Without a expander ball the neck is supported during the sizing operation both on insertion and withdrawal.
My theory is that when withdrawing a expander ball the neck is only contacted by a small amount of the ball when the case is being pulled down out of the die and at a point where the neck is not being supported by the die walls. The case is being pulled down by the rim contacting the upper part of the shellholder. If the ball has more friction on one side than the other or the upper part of the shellholder allows the case to tilt because of a uneven rim the neck could be pulled out of alignment by a small amount.
When using a mandrel the neck is expanded on the upstroke with the case head being pushed down against the shell holder base and less likely to tip to one side. A square casehead and shellholder definitely comes into play here. I like to flush the shellholder out occasionally with spray electrical contact cleaner or isopropyl alcohol
Just theory but removing the expander ball sure seemed to cut down on alignment issue in my bushing dies and going to the expander mandrel seems to add another layer of consistency. Going back to non bushing dies just removed one other variable which could throw the neck alignment out. Add in that I can get mandrels in .0005 increments and it really allows me to fine tune the process and I am a convert to two step sizing
Once again only applicable for shooters who are going for sub .5 MOA precision
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