Neck size clarification

UndFrm · Dec 11, 2024

Hi

Fairly new to reloading, so assume I know nothing lol.

Reloading for a 6mm Dasher, and the dies I have other than the seating die are:

Forster FL die (with expander ball)
Redding neck size die with bushing

I have been told that the Forster FL die is over working the brass because it first contracts the neck and then expands it using the expander ball. It does have the removable expander ball. Is there a point in me getting a Redding FL sizing die with bushing? The idea is that I can remove the bushing and just do the shoulder with nothing to the neck, or if I need to size the neck, I can pop the bushing back in. OR, can I just remove the expander ball from the FL die and just do the shoulder + neck contract?

I do have a few questions regarding if and when I should be sizing the neck.
1. If my twice fired brass chambers without an issue, I am guessing that I don't need to bump the shoulders for any reason. Does this mean that I can just use my redding to size the neck and then seat the projectile? If I am not bumping the shoulder, do I even need to size the neck or can I just go straight to seating? (I am thinking not, as the neck might not adequately hold the projectile).
2. Is it recommended to get the mandrel die to expand the neck? If so, what would the steps look like? Will I be sizing the neck with the redding die (assuming I don't need to bump the shoulder), and then use the mandrel to expand? If I do need the bump the shoulder, my current Forster die also sizes the neck. Will the mandrel die be useful in this scenario?

Basically it comes down to if I should be getting the Redding FL die with bushing and/or mandrel die for neck expansion?

Thank you

TheOfficeT-Rex · Dec 12, 2024

UndFrm said:
I have been told that the Forster FL die is over working the brass because it first contracts the neck and then expands it using the expander ball.

It could be, or it could not be. Pop the expander ball out, then size a case and measure the neck OD across a couple spots. Then resize the same case again with the expander ball in the die, and remeasure. The difference will tell you how much it's being 'worked.'

UndFrm said:
1. If my twice fired brass chambers without an issue, I am guessing that I don't need to bump the shoulders for any reason. Does this mean that I can just use my redding to size the neck and then seat the projectile? If I am not bumping the shoulder, do I even need to size the neck or can I just go straight to seating? (I am thinking not, as the neck might not adequately hold the projectile).

Need? Not necessarily, but maybe- if you shoot in field conditions/wet weather/need every round to chamber, most people will full length resize every time.
Unless you're stripping the bolt to measure chambering force/interference, grab some form of shoulder comparator to see how the shoulder is actually moving when you fire and resize.

Yes, the neck needs to be resized after firing, with either the full length or neck only die, or it wont hold a bullet with the proper tension. If you can seat a bullet in a fired, un-resized case, there are other things you should probably investigate before continuing.

UndFrm said:
2. Is it recommended to get the mandrel die to expand the neck? If so, what would the steps look like? Will I be sizing the neck with the redding die (assuming I don't need to bump the shoulder), and then use the mandrel to expand? If I do need the bump the shoulder, my current Forster die also sizes the neck. Will the mandrel die be useful in this scenario?

The mandrel replaces the expander ball, and adds another step in either process -Resize case/neck without the expander ball in the die(sets case body dimension and squeezes the neck down), then run the brass through the expander mandrel die (open case neck back up to desired final inner dimension).
As opposed to one press step - resize case pulling press handle down (sizes body and squeezes neck) and opening neck as the press handle comes up (expander ball pulls back through the neck and sets the neck size).
Some people like them and think they help, others don't.

... That's a whole lot of words to just tell you "maybe," eh?

Rocketmandb · Dec 12, 2024

UndFrm said:
2. Is it recommended to get the mandrel die to expand the neck? If so, what would the steps look like? Will I be sizing the neck with the redding die (assuming I don't need to bump the shoulder), and then use the mandrel to expand? If I do need the bump the shoulder, my current Forster die also sizes the neck. Will the mandrel die be useful in this scenario?

Short answer is "yes."

Why?

An expander ball and mandrel do essentially the same thing: they both open up the neck as they pass through. The difference is:

- The expander ball is part of the sizing step and opens up the neck as the case is being backed out of the die - so it's inside and being pulled through.

- The mandrel is a separate die (so a separate step) and opens up the neck as it enters - so it is being pushed in.

If they do the same thing, why do an extra step?

First, brass is 2.5x stronger in compression than it is in tension. This means that, depending on a number of factors, you are much more likely to affect the shoulder when you're applying force pulling the expander ball back out of the case. You can elongate the case pulling it through, providing less consistency to the shoulder bump. Pushing in a mandrel is less likely to have an impact.

Second, most, though not all, expander balls are more football shaped. Mandrels tend to look more like a high-BC bullet (much more streamlined profile). This means that mandrels apply less longitudinal force to the neck per distance traveled, meaning they are less likely to deform the shoulder as they expand. Combine that to the brass being stronger in compression thing, and you get a double whammy.

Third, most, though not all, sizing dies do not have different sized expander balls for when you want to play with differing interference fit (what most people call neck tension). You can get mandrels in .0005" increments for common bullet sizes.

UndFrm · Dec 13, 2024

TheOfficeT-Rex said:
Yes, the neck needs to be resized after firing, with either the full length or neck only die, or it wont hold a bullet with the proper tension. If you can seat a bullet in a fired, un-resized case, there are other things you should probably investigate before continuing.

EDIT: Disregard this.

So....
I was able to seat the projectile without sizing the neck. The tension may not be... ideal but I wasn't able to pull the projectile out with bare hands.
I'll neck size the rest, but as you suggested, what should I be investigating now?
The brass is a twice fired, not size but annealed. The bolt closes without much resistance (just a little).

Thank you for the write up. It was really helpful.

Pete B · Dec 13, 2024

If you can seat a projectile, in a fired case without resizing the neck...... then you have some weird shit going on mate, or you need stronger fingers?

UndFrm · Dec 13, 2024

UndFrm said:
So....
I was able to seat the projectile without sizing the neck. The tension may not be... ideal but I wasn't able to pull the projectile out with bare hands.
I'll neck size the rest, but as you suggested, what should I be investigating now?
The brass is a twice fired, not size but annealed. The bolt closes without much resistance (just a little).

Thank you for the write up. It was really helpful.

Disregard this. Must be a one off. I am Infact able to pull out the projectile.

Thank you

UndFrm · Dec 14, 2024

Rocketmandb said:
Short answer is "yes."

Why?

An expander ball and mandrel do essentially the same thing: they both open up the neck as they pass through. The difference is:

- The expander ball is part of the sizing step and opens up the neck as the case is being backed out of the die - so it's inside and being pulled through.

- The mandrel is a separate die (so a separate step) and opens up the neck as it enters - so it is being pushed in.

If they do the same thing, why do an extra step?

First, brass is 2.5x stronger in compression than it is in tension. This means that, depending on a number of factors, you are much more likely to affect the shoulder when you're applying force pulling the expander ball back out of the case. You can elongate the case pulling it through, providing less consistency to the shoulder bump. Pushing in a mandrel is less likely to have an impact.

Second, most, though not all, expander balls are more football shaped. Mandrels tend to look more like a high-BC bullet (much more streamlined profile). This means that mandrels apply less longitudinal force to the neck per distance traveled, meaning they are less likely to deform the shoulder as they expand. Combine that to the brass being stronger in compression thing, and you get a double whammy.

Third, most, though not all, sizing dies do not have different sized expander balls for when you want to play with differing interference fit (what most people call neck tension). You can get mandrels in .0005" increments for common bullet sizes.

I do have another question.
Considering, I am bumping the shoulder and then using the neck size die with the bushing to bring the neck to a consistent measurement. Now, if my projectiles are seating fine, why do I need to expand the neck, using the ball or the mandrel die? Is it only if I decide to change the neck tension and go with a different measurement of the neck?

Thank you

Rocketmandb · Dec 14, 2024

UndFrm said:
I do have another question.
Considering, I am bumping the shoulder and then using the neck size die with the bushing to bring the neck to a consistent measurement. Now, if my projectiles are seating fine, why do I need to expand the neck, using the ball or the mandrel die? Is it only if I decide to change the neck tension and go with a different measurement of the neck?

Thank you

Unless you neck turn your brass, even the best quality brass will have neck thickness inconsistency. When you size the neck down, those inconsistencies will move (mostly) to the inside of the neck where they impact bullet seating. By running a mandrel or expander through afterward, those inconsistencies now move (mostly) to the outside of the neck where they have minimal impact on seating.

straightshooter1 · Dec 14, 2024

Rocketmandb said:
Unless you neck turn your brass, even the best quality brass will have neck thickness inconsistency. When you size the neck down, those inconsistencies will move (mostly) to the inside of the neck where they impact bullet seating. By running a mandrel or expander through afterward, those inconsistencies now move (mostly) to the outside of the neck where they have minimal impact on seating.

Not only can it impact bullet seating, but also bullet release and the way the blowby happens as the bullet is being released. It's a very very small impact that's part of a rather lengthy chain of issues working together. Since turning my brass really just a one time operation, I choose to do it. . . even though I can't really measure the benefit.

Rocketmandb · Dec 14, 2024

straightshooter1 said:
No only can it impact bullet seating, but also bullet release and the way the blowby happens as the bullet is being released. It's a very very small impact that's part of a rather lengthy chain of issues working together. Since turning my brass really just a one time operation, I choose to do it. . . even though I can't really measure the benefit.

I was going to go there, but didn't want to open that whole can of worms in this thread

UndFrm · Dec 14, 2024

straightshooter1 said:
Not only can it impact bullet seating, but also bullet release and the way the blowby happens as the bullet is being released. It's a very very small impact that's part of a rather lengthy chain of issues working together. Since turning my brass really just a one time operation, I choose to do it. . . even though I can't really measure the benefit.

A quick follow up, wouldn't turning affect the life of brass considering it's removing material from the neck? In other words, would it not cause the neck to crack sooner than not neck turned brass?

Thank you

straightshooter1 · Dec 14, 2024

UndFrm said:
A quick follow up, wouldn't turning affect the life of brass considering it's removing material from the neck? In other words, would it not cause the neck to crack sooner than not neck turned brass?

Thank you

Unless one is wildcatting to make the the necks much thinner (like removing .003" or so), it won't affect it enough to be noticed or even be measurable. Like in my case, I'm only removing from .001 to .0015" where that's on the thickest side of the neck and hardly any on the thinnest side. Some cases are a little more uniform, so the range for the amount being removed is even less. So, it's not really going to crack sooner. . . especially when one takes steps to minimize the amount of movement the brass is being subjected to during the firing and resizing cycle. . . . and annealing helps a lot with that too.

UndFrm · Thursday at 4:09 PM

I have an update.
There was significant resistance on bolt close, so I decided to size the brass using Forster FL sizing die. These were the results:
With the expander ball out, neck size of .262
With the ball in, neck size of .267
The neck after seating the projectile is: .268

It seems like 0.268-0.262 = .006, too much tension
On the other hand, .001, too little tension.
Is this correct? Too little and too much tension? I have been told to go for .002 of tension.

The other option is, I fl size the and then use a neck size only with bushing, but wouldn't that be working the brass neck twice?

Or, can I safely go with the .001 tension?

Thank you

Cascade Hemi · Thursday at 4:55 PM

You got Forster'd.

Im2bent · Thursday at 5:10 PM

If you want to you can polish your expander ball to remove .001

straightshooter1 · Thursday at 7:42 PM

UndFrm said:
I have an update.
There was significant resistance on bolt close, so I decided to size the brass using Forster FL sizing die. These were the results:
With the expander ball out, neck size of .262
With the ball in, neck size of .267
The neck after seating the projectile is: .268

It seems like 0.268-0.262 = .006, too much tension
On the other hand, .001, too little tension.
Is this correct? Too little and too much tension? I have been told to go for .002 of tension.

The other option is, I fl size the and then use a neck size only with bushing, but wouldn't that be working the brass neck twice?

Or, can I safely go with the .001 tension?

Thank you

I'd say .006 is way too much even for a cartridge with a neck thickness of .012" or even for something less. There a few things that that's at work with a good "neck tension" that work. .001" can work just fine in a bolt gun, but one may not want to use mag feeding as recoil may cause the bullets in the mag to change seating depth during firing. With a 6mm Dasher, there may not be recoil to be of concern, but an issue not to be ignored. In addition to this, the size of the bullet and how far it's seated into the case contributes with this issue.

There are some shooters who've used almost zero neck tension so when they chamber their round, which is hand fed, the bullet is pressed into the lands and the bullet also pushes into the case. Their reasoning is that they get very consistent velocities this way and don't have to worry about throat erosion. So, having little or no neck tension isn't really "dangerous", but it could be a problem if you have to eject a live round where the bullet is pulled out of the case and the powder spills into you're trigger assembly.

In my .308 I've gotten good results with .0015 neck tension and have had no problem. . . though as I mentioned, I'm hand feeding those cartridges.

The only issue I have with using an expander ball in my Forster FL sizing dies is that the ball pulls on the neck causing the shoulder to change its headspace measurement and makes for less neck runout. This can be mitigated if the amount of reduction is reduced. Like your necks are .262 with no expander ball and the ball will expand it by .005" and if you have the reamed where the die only reduces them to .265, there's less tending to pull on the shoulders and less tendency to induce a lot of runout.

You don't have to size twice with a bushing die as you can control the amount the necks are being reduced before the ball is pulled through. But busing dies just tend to produce more runout than a FL sizing die that uses not bushing.

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