Setting neck tension with expander mandrel and bushing die questions

[antelopedundee]

Here is caliber specific Mandrels.
available in .0005" increments in calibers 22 to 338 and will range from .001" above bullet diameter to at least .003" below bullet diameter

Caliber Specific Expander Mandrels

21st Century Shooting, Reloading products, Caliber Specific Expander Mandrels

www.xxicsi.com

Awesome the way that they are marked.

 

[65WSM]

Whidden has been very helpful with dies for my wildcats. They will come up with an expander ball to provide what you decide you need for neck tension.
I use the K&M expander the most. That is because they have a window riser to help you see what is going on. Most often, I only expand the necks of new cases before firing. Neck tension is an important accuracy variable. After you have decided on an overall length, try different neck tensions. The most important thing is to have the same neck tension, time after time. You may have to turn necks to get this consistency.
Don't forget the honed Wilson bushings. They are tapered a half of a thousandth. You can seat them upside down in your bushing die and get a different neck tension by half a thousandth. I want to credit Slick8. Good advice.

 

[30BR]

Yeah new brass would have needed to be sized regardless.

Just run it ththrough the mandrel which will give you .001 under cal.

If using a mandrel it really doesn't matter if you use a bushing or standard die as it will under size it then you'll set final tension with the mandrel.

To get the best results, you're to want to anneal otherwise you'll eventually work harden the brass which will cause spring back on your neck dimension.

It would be best IMHO to use the FL sizer first, rather than the Bushing die, since the FL sizer tends to get the entire neck sized down to the shoulder, while the bushing leaves a bit unsized.

 

[Bobcape]

This deals with ES mainly, but he does talk neck tension. Might be helpful.


Bob

 

[HERMAN8R]

Agree with 65WSM. K&M makes mandrels to your spec

Expand Mandrel Selector and Accessories | Reloading

Expand Mandrel | Expand Iron Tool will iron out and slightly expand the case neck. The brass will spring back to the size needed to neck turn your brass.

kmshooting.com

Expand Mandrels for Bullet/Neck Tension Builder

Expand Mandrels for Bullet Tension expand the case neck so the brass will spring back to the correct size needed for seating bullets.

kmshooting.com

Check out their download for tool instructions when ordering

They make great products & have great customer service.

 

[cdherman]

Fine print on the video ( I did not watch it) notes inside neck dry lube. That is what I started doing after reading about it somewhere. I read about it in a thread by some real accuracy nuts -- they were discussing how they got LESS accuracy when they cleaned their brass too much, and better with some powder residue. Then one fellow revealed he was using powdered graphite with good results.

Anyhow, I suspect there are numerous different mandrels that fill the bill. I have been pleased with Sinclair, but I also anneal and tend to shoot expensive brass. I But the inside neck prep is important, and I lube ever neck before running the mandrel inside with graphite. I've read discussions where experienced reloaders have paid attention to the seating force required and whenever it seemed "off" they would put those rounds to the side. When later shot, somewhat unsurprisingly, the ES and accuracy of the "outliers" was off considerably.

This was my drive to move to mandrel sizing.

 

[Mikecr]

The Sinclair Expander (not turner) mandrel is a pretty good size. Best IMO would be right at cal diameter.
What folks should be noticing and learning here is that without use of an expander -you're just forcing your bullets to do that function.
That is if you leave higher than standard springback from cal interference, your seating bullet will just finish the expansion. So it doesn't buy you anything to to do that, much less doing it in extreme.

As far as partial neck sizing -vs- FL neck sizing, unless for an underbore (like a 30br) FL sizing of necks is the worst thing reloaders have ever done.

 

[Philward]

I thought the point of using the bushing sizer was to remove the expander from the process, eliminating the chance of stretching the cases a little while pulling it out of the die. Which I guess that assumes you know the dimension of the chamber neck and the case neck is a uniform thickness around the circumference and your bushing is the exact size you want to give you the neck tension you desire. To use the expander as well seems to induce a possible error you cannot control.

 

[30BR]

I thought the point of using the bushing sizer was to remove the expander from the process, eliminating the chance of stretching the cases a little while pulling it out of the die. Which I guess that assumes you know the dimension of the chamber neck and the case neck is a uniform thickness around the circumference and your bushing is the exact size you want to give you the neck tension you desire. To use the expander as well seems to induce a possible error you cannot control.

I use a bushing f/l sizer to bring the neck down (without an expander) just to a point where the sizing expander (on my neck only die) can true the ID to the dimension I want so that any irregularity in the neck is pushed to the outside. Yes, your setup needs to make concentric ammo.

 

[HERMAN8R]

Mikecr, are you suggesting to neck size only with a bushing 2 to 3 thou less and then use the caliber size mandrel after that?

 

[Mikecr]

I thought the point of using the bushing sizer was to remove the expander from the process

No, that's not it.
Neck expansion is important. You might see it as a 'Pre-Seating' action.
It drives thickness variance outward, away from seating bullets, and ideally it sets correct interference for seating bullets.
Expander mandrels provide better runout than expander buttons, as they don't pull necks out of whack.

Brass holds energy (all that we add). Anything holding energy seeks a lowest state of that energy.
We see this as spring back, which continues over time & opposite last energy added.
With this, it's better to have necks trying to spring back inward(against seated bullets), over time, than to have them freely spring back outward, reducing bullet grip, over time.

The purpose of bushings in neck sizing is to provide adjustment for correct downsizing amount and length. You can dial in perfection, and with a descent chamber and a plan, you can produce very low runout ammo with bushings.
Replace button expansion with a mandrel, and the right bushing, and runout drops even further, and neck tension will be consistent.
Most bushing dies provide partial neck sizing length, which is good because you should never size greater length than seated bullet bearing. And bullet bearing should never be seated FL of necks. You can finely tweak loads with length of bushing sizing, as this is your actual neck tension adjustment (not interference).

Perfect neck sizing would downsize fired necks for 1 to 1.5thou under cal interference(after spring back). The perfect mandrel expansion for pre-seating would be at cal (not under, not over). The mandrel would then expand thickness variance outward, with the rest of the neck minimally upsized (~1/2thou) as well.
On mandrel removal normal hardness necks would spring back inward ~1/2thou, ready for bullet seating.
This leaves full spring back force gripping seated bullet bearing times the area chosen (sizing length).
Those thinking more interference here equals more tension -are wrong. Seating bullets will just finish the job described, removing that excess interference.

Where things change dramatically is with actual FL sizing of necks, or with any sizing length greater than seated bearing. This leaves unexpanded interference binding against bearing-base junction of bullets, hugely increasing tension, and variance of it. Unless shooting an underbore that needs this to reach extreme pressure peaks, then don't ever do this. There is no 'good' in it,, only bad.

 

[Carbine Kid]

I don't use the bushing die approach, but it seems to this observer that if one used the proper size bushing that that would obviate the need for an expander mandrel. Of course that would be better if your cases had uniform wall thickness in the neck.

I agree with this.
By turning my necks a variable is eliminated. Then neck size to .002 neck tension with a Redding bush die. I have been able to consistantly shoot 1.5 inch groups at 500m with a 6x284.
Removal of as many "variables" as possible is the key to LR shooting and in my opinion, starting with the neck is good place to start.
All the best with your work up.

 

[Philward]

I see, the difference in the mandrel vs button expander, mandrel expands the neck while being inserted into the case while the button expands while being withdrawn from the case-if it is used as part of the initial sizing. Another added step to the reloading process...

 

[antelopedundee]

I agree with this.
By turning my necks a variable is eliminated. Then neck size to .002 neck tension with a Redding bush die. I have been able to consistantly shoot 1.5 inch groups at 500m with a 6x284.
Removal of as many "variables" as possible is the key to LR shooting and in my opinion, starting with the neck is good place to start.
All the best with your work up.

Depending upon how thick your necks are after turning, [I try to get them around 0.014 or so] and the neck diameter of your sizing die you may not need to do any neck expansion after sizing. If you end up with .003 or less under bullet diameter I'd go with that. I'd use the Sinclair mandrels interchangably as expanders if I needed to.

If one is using the Redding competition seat dies, they are somewhat delicate and not recommended to be used with compressed loads or too tight necks.