Proper use of expander mandrels

[Dave Marshall]

I have read that using expander mandrels is the best way to ensure consistent neck tension. So I’m going to give it a try.

My question is: what is the proper way to use the mandrels?

I purchased Whidden bushing dies, bushings, and his expander mandrel kit. The bushing part of the process I am familiar with, but could use some advice on the use of mandrels.

Do the mandrels simply go in place of the ball on the decapping stem of the sizing die?

How much do I want to be sizing the neck down with a bushing before expanding it on a mandrel?

I decapp and size on a Dillon 650. Adding another tool to the tool head is no big deal. I also anneal after each firing.

 

[Milo 2.0]

Do you mean you bought the expander ball kit? Mandrels need their own special die body.

 

[Dave Marshall]

Do you mean you bought the expander ball kit? Mandrels need their own special die body.

It’s the expander ball kit I bought.

I guess the only question is really how
much difference do I want between the bushing and expander?

 

[Milo 2.0]

Ok, they just replace the expander ball on the stem.

 

[Fliers]

.001 difference. Just enough to push inconsistencies to the outside. But not enough to induce runout.

 

[avidflyer]

I have these dies, you'd be surprised at how much they size the neck down before expanding. Size a piece with no expander then measure. I use a pin gauge and also take OD measurements. I talked to John about this on a set of custom 308 dies and they couldn't open the neck up enough for my liking for the 308. It works ok, but SOME not saying all really work the brass. In the long run its a great set up. Just need to take measurements and know where you are

 

[Dave Marshall]

I have these dies, you'd be surprised at how much they size the neck down before expanding. Size a piece with no expander then measure. I use a pin gauge and also take OD measurements. I talked to John about this on a set of custom 308 dies and they couldn't open the neck up enough for my liking for the 308. It works ok, but SOME not saying all really work the brass. In the long run its a great set up. Just need to take measurements and know where you are

I use a bushing die. Bushings are available in every imaginable size.

 

[avidflyer]

I use a bushing die. Bushings are available in every imaginable size.

John makes bushing dies, and also non bushing with a set of six or eight swappable expander tapered buttons/balls. Which are you trying to use.

2 different dies

 

[Dave Marshall]

I have the bushing dies, several bushings, and the expander kit. I have everything I need.

 

[Uncle Ed]

You stated you did not want to turn the necks, you will need to know how much neck thickness variations you have. Then experiment with bushing size and expander size for the desired amount of bullet grip.
I use the Redding neck thickness gauge and one turn of the wrist will tell you the total thickness variations. This is faster than using a vernier ball micrometer and taking several thickness measurements.

Tech Line & Tips (FAQs)
Bushing Selection
https://www.redding-reloading.com/tech-line-a-tips-faqs/140-bushing-selection

"If the neck wall thickness varies more than 0.002", it may be necessary to use a bushing a couple of thousandths smaller than your calculations indicate, and then use a size button in the die to determine the final inside neck diameter."

NOTE, in the same Redding bushing FAQ it also tells you if you reduce the neck diameter .004 or more you can induce neck runout. And if the necks are not turned the runout will be even more. Bushing dies work best with tight neck chambers and neck turned brass. And this is why the Lee collet die is so popular, because you can reduce the neck diameter more with very little neck runout. Or just use a Forster full length die with its high mounted floating expander.