I am having a problem with my Redding neck sizer die. It is giving me more runout than I would expect it should. Press is a RCBS Rockchucker. I am using an o-ring on the die so that it “floats”. I had heard that the o-ring can help to reduce runout. I have not tested it with the standard lock nut. Fired cases have less than 0.001” of runout on the neck. They have less than 0.001” variance in neck thickness as well. But when I run them through the die (it has a carbide sizer button) they come out sometimes with 0.0035” of runout. 0.003” is common. I removed the carbide button and runout was still about 0.00275”. I use moly powder when neck sizing. I cleaned the die with a q-tip and checked again and runout was still about 0.003”. So what might the problem be? I have heard that as runout increases so will group size. Is there any ballpark figure? Like if the gun shoots 0.5” groups with 0 runout what would group size be with 1, 2, 3 thousandths of runout? Thanks, Rufous.

Never had much luck getting microscopic runout measurements with a neck sizer. When I tried using a neck sizer the best I got was .003. If other folks know the secret to getting better runout, please let us in on the secret. Try doublechecking the setting on your neck-sizing die and make sure you have it adjusted down far enough(but not too far). One trick I use on my press is to free-float the shellholder with an O-Ring. Tightened up runout .001 or so.
My cutoff point for my good ammo is .003. Unless you are trying to shoot the backhairs off of a flea at 500yds you probably won't notice the difference between ammo with .001 runout vs .003 runout

Good Luck
ZM

Turning the necks is the key. But I have a better solution, the Lee Collet neck die. Since buying the Lee die my Redding S neck dies have gone unused. With the Lee Collet neck die I get runout of around .001 or less (measuring on the bullet).

RUFOUS,
I've had this same problem. The cure I've found that helps is to screw the die down against the shell holder until the ram just rolls over the top of the stroke. With the ram still raised, I lower the lock ring tight against the press and tighten the locking screw. After the ram is lowered I will use a wrench to loosen the die. When the die is screwed into the press, the die should come to a sudden dead stop. Not tighten down gradually. If the die does seat gradually it is because the die is not in true alignment to the ram or press and is misaligned. If you don't want the die to bottom against the shell holder, put a feeler gauge between the shellholder and the die. This helped cure my die caused runout. I also adjust the seating die in this manner. A misaligned seating die will also cause headaches. good luck.

Hi Rufous
I had the same problem with my Foster necksizer in 308win , the runout was usaly around 0,004 on the outside of the neck , but with this simple setu I was ebele to reduce it to 0,0005-0,0015 .
The secret is to use the sizer button as a angling guide in to the sizing portion of the die.( it took me 238 cases to discower this )

The setup is like this .

Make a die setup like BigBoy advised abowe
and then take a fired case and lube both inside and outside of the neck.
Size only half of the neck in your NS-die and stop the stroke.
When the case is still in the die (half sized )
you should screw the threaded rod with the sizer button upp so the button will make firm contact to the inside of the neck , lock the locknut and compleat the stroke.

Now you will get the stright case necks.

If the depriming pin not will reach to eject the primer you will have to deprime before sizing or make a longer pin , the Foster die is constructed in that way you could screw the sizer button individuelly of the lock collet nut of the depriming pin , in that way I can have inside contact and still make the primers come out.

A warning ! if you adjust the sizer button to a case brand with thin neck walls and then try to size another brand that will have thicker case walls you end up with a bulged and wrinkled case.

Try it and let me know how it went.

Anders �sterberg SWEDEN