Tuning sizing dies for low Runout

I have found that I can generally tune my FL/neck dies for lower runout. If I remove the depriming stem then size 4 cases my case neck runout will be on par with fired cases. Next I size the cases with stem and expander installed this is usually where runout is induced. Next I index the stem a 1/4 turn deeper and resize the cases and remeasure runout I do this three more times and generally I can find one of the 1/4 turns that produces only .0005 to .001 in runout. I do lube the inside of the case necks and the lube is an important step. I've tried a small oring under the stem lock ring to float the expander but find tuning the stem produces lower runout for me. I prefer the Sinclair concentricity gauge to trouble shoot runout in my reloading process.

Thanks for sharing your observations. What kind of lube do you use on the inside of the neck? Have you ever tried the Imperial Dry Neck Lube on the inside?

How about since you've found that your decapping pin/expander ball stem is not square it might be an idea to not use that stem & expander ball.

I never use an expander ball. I use a universal decapping die and I don't run a stem in my sizing die at all.

Nothing wrong removing expander and using a lee collet or mandrel expander or bushing dies lots of ways to get the desired results. Just sharing a way to squeeze every bit of accuracy out of dies without extra steps or more $$. Just trying spread a little insight

As far lube I've used the RCBS pad lube on a brush or Q-tip or One Shot sprayed cases shaken so necks are up and get lubed inside same thing for home brew 1 part 100% liquid lanolin mixed with 10 part 99% isopropyl alcohol. I've never tried the imperial wax or dry graphite I even have a can of graphite but the potential for a huge mess in my reloading room has kept me from fooling with it.

One of the biggest causes of case neck runout is caused if the expander is locked down off center.

I use Forster full length benchrest dies with their high mounted floating expanders. And they greatly reduce and neck runout because the case neck is held and centered in the neck of the die when the expander enters the case neck.

I retrofitted my RCBS and Redding dies with the high mounted Forster expanders to reduce neck runout.





Another method is to remove the expander from your dies and use a expander die to reduce neck runout.

And now Ripley's believe it or not.............use Lee dies.

Below the locking collet on the Lee dies holds and centers the expander. Meaning the expander can not be locked down off center. Just clean up any burs and metal fragments in the collet that might cause the expander to tilt. Also note the expander is located higher up on the Lee dies and helps reduce any neck runout.

Good info any little tricks are appreciated the more I know the better.
I remove the depriming stem and expander ball from all my dies. Deprime with a universal die so I don't get crud in my sizing dies. After neck turning for a bench gun I now use a k&m expander mandrel then neck turn all my cases even for hunting rifles. I know exactly what neck tension bushing I need before ever loading a round this way. Not for everyone but it has given me the best results across the board on all my rifles.

Thanks for the tips. I use an expander ball that is smaller than caliber when I resize my brass (.30 cal for the .340, .270 cal for the .30, and .243 for the .270 cal). That way the case still gets deprimed, but the expander ball does not stretch the case when I am removing the case from the die.

I still tune my Forster dies and I also have had good luck with some Lee dies they do tend to need a little polishing. I have a Lee 223 sizing die that throws very little runout and I had a Lee 6.5 creedmore die that no amount of tuning and polishing would reduce runout so I just picked up the Forster FL die to replace it and their micrometer seater to play with.

Just say no to expander buttons, this has been covered a lot. Don't use them and say good bye to brass problems!

BallisticsGuy said:

How about since you've found that your decapping pin/expander ball stem is not square it might be an idea to not use that stem & expander ball.

I never use an expander ball. I use a universal decapping die and I don't run a stem in my sizing die at all.

Click to expand...

BallisticsGuy-If you don't use the expander stem, how do you size your necks? I removed my sizing expander stem and ran my brand new Lapua cases up into the die-it took the neck I.D. to .290-I was unable to use my LEE Collet neck die nor could I use my Expander ball on the stem when I re-installed it. I had to wait for an expander mandrel, which I just used, now my runout is absolutely horrible.

Use a bushing die and not an FL die so you can control the amount of downsizing.