Expander Mandrel Size?

[Cs22]

I've learned a ton of knowledge from you guys already, but I feel I need some opinions on my reloading process. I'm a new reloader and I purchased a lee die set to help save money for the rest of the reloading equipment.
After resizing with the expander ball my neck tension is varying up to .0025. In reloading for an ar platform and I'm wanting to avoid crimping as well as get more consistent neck tension.
I'm considering removing the expander ball and using and expander mandrel from 21century. The smallest they have is 0.261. Would this give enough neck tension after spring back. I've read many of you dont like less than .003 neck tension for gas guns.

[A5BLASTER]

What is the cost of the mandrel? If it's close or a bit mire then a hornady grendel sizeing die. I would just upgrade my die.

[Bobke]

[Klem]

Cs22,

Are you using the same manufacturer of brass? If not this might account for the variation in neck tension.

I use Lapua brass which has a consistent thickness of 0.013-0.0135" measured at four points of the compass around the mouth. Lapua is thicker than other brands. I use a Forster sizing die without the expander mandrel, so the outside of the neck is sized only. It imparts .003" of tension, measured by what the OD is after sizing and after seating. This is fine for an auto loader. If the bullets are moving on being loaded into battery they are not making any difference to group sizes.

The OD of the case neck is;
After sizing .2865
After seating, .2895
After firing, .2935

I don't anneal.

[centerfire]

I've learned a ton of knowledge from you guys already, but I feel I need some opinions on my reloading process. I'm a new reloader and I purchased a lee die set to help save money for the rest of the reloading equipment.
After resizing with the expander ball my neck tension is varying up to .0025. In reloading for an ar platform and I'm wanting to avoid crimping as well as get more consistent neck tension.
I'm considering removing the expander ball and using and expander mandrel from 21century. The smallest they have is 0.261. Would this give enough neck tension after spring back. I've read many of you dont like less than .003 neck tension for gas guns.

.0025" ID is a lot of case variation. I would recommend figuring out why you have so much prior to mandrel sizing. Assuming you aren't mixing brands of brass or once fired and five fired cases, you'd likely have just as much neck size variation after sizing with a mandrel.

[Cs22]

Yes, that's exactly what I thought. All my brass is once fired Hornady Black brass. I intend to try what Klem does and resize without the expander and check for neck tension and uniformity

[Klem]

Cs,

If you are then just be aware it is a hit and miss thing. I have two sizing dies; a Forster and a Redding. Without the expander ball the Forster imparts .003" of tension while the Redding only gives .001". The Redding is not enough for an auto loader without extra crimping.

It'll only take you 10 minutes to figure it out with the die you have.

[Cs22]

Yea, I'm thinking I will either have to buy an expander mandrel or a new die. Sizing without the expander is measuring about .011. That's way to much neck tension I would assume. Neck tension with the expander is some times in the .001 range so I'm afraid it wouldn't be enough. Would the .261 mandrel after sizing without the expander leave enough neck tension?

[Cs22]

The three rounds I fired and sized without the expander seemed to be a lot more consistent by the way.

[Klem]

Cs,

.011 of difference between a sized neck and a seated neck sounds harsh. It won't help case life with overworked necks.

Can you confirm the three outside diameter measurements on your rifle please, using the Lee sizing die without the expander button.
After sizing,
After seating,
After firing,

Brass is only elastic to a degree. Your .011" will not be 4 times the grip of say .003". The seating bullet will act as an expander mandrel and end up with a fixed amount of maximum grip.

[Cs22]

Ok, just did some measuring. I hope im not giving you guys bad information because I havent seated any bullets yet. I'm measuring od of new Hornady black 123 eldm.
The new hornady black od measures .289
Fired od measures .300
Resized od without expander is .279
Resized od with expander is .287 ish

[Klem]

Cs,

Interesting, that Lee sizer is working your brass like Conan the Barbarian.

The neck of your chamber has been generously reamed (.300-.301). Fired cases are then squeezed to .279 which is .021" of squeeze/stretch. Doing this every time is going to work-harden and split the neck. I would ditch the Lee sizer and get a better one: Forster, Redding, Hornady.

[centerfire]

Stop measuring OD, you're adding in the neck thickness variation of the brass to a measurement that shouldn't have it. Turn you calipers over and measure the ID of the brass. Then measure the OD of the bullet and subtract the two. Properly annealed brass only needs .003 of neck interference. I use a .262 mandrel and get .003 interference. Rock hard brass will have more spring back and may yield greater interference from the same mandrel (.005 for example).

[Klem]

Centrefire,

Let's not get into your familiar online 'showdown'. Neck thickness is a non-issue when you are measuring the difference between before and after seating.

Rock hard (hardened) brass has less springback than fresh brass. It does not have the ductility to grip the bullet like fresh brass does. The bullet acts as a mandrel and swages the neck when seated but is then held with less grip than fresh brass.

Cs,

Feel free to continue measuring OD. You can use Centrefire's technique or mine; they measure the same thing.

[Cs22]

Yea, that's what I was afraid of. I guess it's true what they say. Buy once, cry once. Im considering a redding type s die. With my chamber though that would mean a jump of about .014 to get .003 neck tension? Is that possible with these bushings?