How to choose a bushing size?

[bigedp51]

Please Elaborate.

How much is the neck reduced in diameter with a standard factory SAAMI chamber and using a bushing die.

A bushing floats in the die and can move from side to side and even tilt when reducing the neck diameter. Meaning in a off the shelf factory SAAMI chamber you are better off using a standard full length non-bushing die.

If you think you are over working your necks then buy a Forster full length die and have them hone the necks.

 

[Mikecr]

There are 3 potential advantages with partial length neck sizing using bushings. This, with 3 different reloading attributes associated with necks.
1. Tension control
The first thing to understand here is that neck tension is neither interference fit nor friction. Tension is the grip force provided by spring back, on an area of seated bullet bearing. And since spring back itself is no more or less than provided by your brass, the adjustment to tension is via area the spring back force is applied to grip bullets. Normal bushing dies partial length size necks, and the length of this sizing is die adjustable.
2. Runout
The first thing to understand here is that neck sizing should always include pre-seating expansion. Even if a separate operation. You're not supposed to be sizing down using bushings without following this action with expansion.
Where you expand necks ever so slightly, and the best in this regard is with separate expansion mandrel, your thickness variances will be driven outward -away from seating bullet bearing. Since your necks are slammed straight with fire forming, and not FL sized with bushings, there is a reliable bottom portion of necks that is held as dead straight. Combined, loaded runout as measured off exposed bullet bearing, can be expected as very low.
3. Sizing control
When we size brass, we're adding evil energies to forever change that brass. There is nothing 'good' in this, and in every way it's best to reduce this to the minimal amount necessary. A great thing about bushing selection is that it allows you to do just that.
You're not stuck with oversizing, or undersizing necks. You don't have to seek a custom die to get this right.
Seat a bullet, measure loaded neck OD, subtract 3thou from this for a bushing that will get you **** close to perfect. If this takes a neck 3thou below cal, the neck will spring back (outward) to ~2thou under cal. Then a pre-seating mandrel at cal would bring the neck to cal, where it would then spring back to ~1thou under cal. Perfect and ready for seating of bullets.
If your were to pull the bullet from that test for loaded neck OD, you'll see that it springs back ~1thou (max). That is the grip you have, even if you selected a bushing that way oversized and did not followup with pre-seating expansion. In that case you simply used a soft bullet for re-expansion, which you should never do.
Bullets are NOT for sizing, and over working of necks is neither good for runout, nor consistent tension.

There are a lot of other circumstances & details leading to a bit of trial & error in bushing/mandrel selections. Enough so that it would be better in another thread.
But you can be rest assured that there are plenty of reloaders out there that are successful and happy with bushing neck sizing.
As far as body sizing requirements, again, this would be another thread, but because it's another subject all together.

 

[Deputy819]

I have had excellent results using bushings that reduce neck I.D. by .003". Then, setting neck tension with a .002" under caliber mandrel, not the expander ball.

This is my process as well. I use the titanium nitride turning mandrel from 21st Century. I don't turn necks.

 

[AZShooter]

LSherm,

Darn I forgot to mention the use of a bushing AND a sizer ball for necks that were not turned that have some thickness variances. Thanks for reminding me and others. The Redding bushing die comes with a decapping rod and two sizer balls. Well really one sizer ball and an undersize one to hold the decapping pin in place. I have used the smaller ball for so long I forgot about the actual sizer ball.


Dok7mm thanks for the idea of using a mandrel for final ID sizing. Where would someone buy an undersized sizer mandrel?

There is such a thing as a custom "fitted die" that would work with a specific brand of brass if it had consistent wall thickness. It would eliminate the oversizing that happens with a standard FL die. Standard FL die is purposefully made to accommodate any thickness brass made. It reduces the OD of the necks an extra amount so even the thinnest brass will have neck OD reduced. Then the sizer ball opens it back up for proper neck tension. The "fitted die" would have a larger neck dimension to mildly reduce neck OD then, of course, the sizer ball would finish the sizing.

There is also a fitted die that could size the necks without a sizer ball. Realistically the necks would have to be turned to make it work without the ball. I have a 30 BR with a tight necked chamber. I use a standard 30 BR RCBS FL die without the sizer ball but I turned the necks to match the die. May sound strange to work backwards but I used this setup to try the method Virgil mentioned in The Houston Warehouse article.

Finally a sizer ball could be made larger or smaller than the usual dimension to tweak neck tension instead of using a different sized bushing. To be honest I don't know where I would go to find a larger sizer ball but supplied sizer ball can be polished smaller.

Bet by now the OP is a bit overwhelmed with the particulars. All he wanted to know is how to figure out which bushing......

 

[Mikecr]

Finally a sizer ball could be made larger or smaller than the usual dimension to tweak neck tension instead of using a different sized bushing.

This in no way affects tension with a bushing die.
Neck tension IS NOT interference fit, it IS NOT friction, or resultant seating forces.
Tension is spring back force gripping an area of seated bullet.

On firing, necks expand to counter this spring back force, to fully release bullets.
And keep in mind, with far less neck expansion than you can measure, a bullet once gripped is free in the wind.
It seems a joke when folks make wild claims about high neck clearance (like 3-4thou) needed 'for safety'. It's not true at all.

Any change to brass dimension exceeding presented spring back causes that brass to yield. So if necks spring back 1thou, and you squeeze them down 2thou they will yield ~1thou. Sizing is actual yielding to a new relaxed dimension.
Your necks will only spring back ~1thou worth of distance. Within that distance is the force available to grip bullet bearing. To cause greater interference for bullet seating (smaller bushing) is not increasing spring back force, nor force distance. The seating bullet will just up size that additional interference, causing yielding, and you're right back where you'd be had you only provided 1thou of interference.
So ideally, you would set 1thou of interference for bullet seating. More or less, does NOTHING for tension.

Where you want more or less tension, you adjust the area spring back force is applying to(gripping). That is LENGTH of interference.

 

[jlvandersnick]

This in no way affects tension with a bushing die.
Neck tension IS NOT interference fit, it IS NOT friction, or resultant seating forces.
Tension is spring back force gripping an area of seated bullet.

On firing, necks expand to counter this spring back force, to fully release bullets.
And keep in mind, with far less neck expansion than you can measure, a bullet once gripped is free in the wind.
It seems a joke when folks make wild claims about high neck clearance (like 3-4thou) needed 'for safety'. It's not true at all.

Any change to brass dimension exceeding presented spring back causes that brass to yield. So if necks spring back 1thou, and you squeeze them down 2thou they will yield ~1thou. Sizing is actual yielding to a new relaxed dimension.
Your necks will only spring back ~1thou worth of distance. Within that distance is the force available to grip bullet bearing. To cause greater interference for bullet seating (smaller bushing) is not increasing spring back force, nor force distance. The seating bullet will just up size that additional interference, causing yielding, and you're right back where you'd be had you only provided 1thou of interference.
So ideally, you would set 1thou of interference for bullet seating. More or less, does NOTHING for tension.

Where you want more or less tension, you adjust the area spring back force is applying to(gripping). That is LENGTH of interference.

Mike
how much of the neck do you typically size (reduce) with the bushing prior to using the cal expander mandrel?

 

[bob4]

Where would someone buy an undersized sizer mandrel?

Just picked 2 up from midway or Brownnells made by Sinclair.

 

[bigedp51]

Expander Ball Kits
https://www.whiddengunworks.com/product/expander-ball-kits-and-sets/

Description
The Whidden Gunworks Expander Balls typically allow the shooter the opportunity to adjust the neck tension from .001″ to .005″. The Expander Ball Kit comes with five Expander Balls. Each kit includes an Expander of the chosen caliber and decreases in size by .001″. Example: If an Expander Ball Kit for .243 caliber is ordered, the kit would include Expander Ball sizes .243, .242, .241, .240 and .239.



Tech Line & Tips (FAQs)
Some Frequently Asked Questions

Question: Do I need to use the expander button that came with my Type "S" Die?

Answer: It is advisable to use an expander button to maintain consistent neck tension if the case necks have not been turned to a uniform wall thickness. However, the expander button can be replaced with the Decapping Pin Retainer (included with your Type "S" Die) if the user does not wish to use an expander button.

 

[Mikecr]

Mike
how much of the neck do you typically size (reduce) with the bushing prior to using the cal expander mandrel?

I start at ~1/2 neck length, and never more than seated bullet bearing. From here I have the option of tweaking sizing length, to shape grouping. With a couple cartridges ~1/3 sized neck length gave me the best results on target, and even that is plenty of grip for my use.

I don't ever put bullet bearing into donut area of necks. And I would NEVER size this area (FL neck size), as it brings it into tension as an unexpanded binding force on the base-bearing junction. Yes that would greatly increase bullet grip, while greatly increasing variance in it. Similar in effect to crimping (which I also would never do). If a cartridge/load needs this kind of starting pressure it's better to test for that with bullets seating into lands. If you need that kind of grip for heavy recoiling and magazine use, well, those were your choices.

 

[jlvandersnick]

Thanks Mike
I find your submissions very detailed, informative and helpful. You approach things from an scientific/engineering perspective, which I have to admit sometimes is a little over my head. Sometimes I have to reread them several times....but I typically am able to figure everything out......partly from shear determination but mostly because you communicate thoroughly and effectively. I have learned a lot on this forum from you and others like you that are willing to share your expertise and experience.

Some really helpful and unselfish people on this site...and I thank you all
Jerry

 

[AZShooter]

Interesting thoughts on neck tension Mikecr. Amount of bullet bearing surface in contact with neck explanation makes sense.

I do have some thoughts and it would be interesting to hear what you and others think.

Donuts:
You mentioned never seating the bullet so deeply as to hit the donut. I didn't think the donut was a common occurrence. I have only encountered the donut once and it require inside reaming, it was a 284 win made into a 6.5-284. If other hundreds of cartridges I have loaded had the donut I never noticed it like that one.



Sizing neck with a .003" interference fit

How about a real world example: Lets talk about loading for a 300 win mag which will be used for hunting. The rifle holds three in mag box. We are going to load 200 gr Nosler Accubonds deeply into the case to fit the mag box. There is full bearing surface in contact with all of that short neck of the cartridge case. The cartridge was sized with a RCBS FL die which sizes the neck OD .003" smaller than the OD of a loaded round. Mike, If I read your explanation correctly you said there would be yielding of the brass and the end result would be a .001" springback force holding the bullet in the case neck.

Quote: "Your necks will only spring back ~1thou worth of distance. Within that distance is the force available to grip bullet bearing. To cause greater interference for bullet seating (smaller bushing) is not increasing spring back force, nor force distance. The seating bullet will just up size that additional interference, causing yielding, and you're right back where you'd be had you only provided 1thou of interference."

If the end result is only a .001" springback, then why would RCBS (and other manufacturers) make a FL die with a .003" difference in sized vs loaded OD? Having made a ton of hunting ammo as well as target ammo, I have tested sized neck reductions of .001", .002" and .003" then leaving a loaded round in the magazine for multiple firings. If the reduction is not at least .002" interference or more with many hunting rifles, the bullet will move in the case.

I have pulled many bullets and the ones that were seated with .001" interference fit vs .003" (both having full bearing surface/neck contact) The .001" fitted bullet pulled out much easier. I would submit that it appears to be more neck tension or holding the bullet in place going on with a neck that is sized smaller.

Perhaps your suggestion of ending up with a .001" springback after any yielding due to over sizing OD to a smaller dimension only works with thin walled BR type brass?
A factor that has not been mentioned is neck wall thickness. It is a factor that IMO would determine just how firmly the bullet is held in place.

All I know is my loads have worked well over the decades with most of the hunting necks being undersized .003". If the round is going into a mag box it gets sized accordingly.

I value your knowledge Mike, Perhaps I and others can learn from this discourse.

Ross

 

[Mikecr]

Seating force, sometimes seen also as pull force, relates to friction. Expanding tighter interference will cause way more friction. The surface of a bullet put through this will be torn up pretty good, raising it's surface profile. The neck won't appreciate this either.
Instead of both surfaces being together as smooth, they're now together as folded sandpaper (grabbing itself). This is also setup for cold welding over time.
You can lube everything more, and if you do there should not be any differences between pull force at 1thou or 3thou sizing. But then, COAL may not hold under heavy recoil and slamming in a box.
When you pull a bullet from necks sized down, the necks still only spring back ~1thou.

Things are also different (tension-wise) when bullet bearing is seated into/through neck-shoulder junction. That junction is forced inward if you size it so, and outward if expanded (even with a bullet), but it's springback & springback force is way different than necks themselves. This is heavily influenced by shoulder angle, which resists change with more leverage. Standard ~1thou does not apply here.
Everyone should know this is not a good scenario for accuracy.

W/regard to donuts, all brass comes with donuts inherent to it's forming. Neck thickness is higher nearest neck-shoulder junction, and thinner outward to mouths. It isn't much, you can usually drop a bullet through it, but there, and brought into play with sizing of it. I say: don't do that.
If you neck turn correctly you'll remove and mitigate future donuts. Then you can put em back with heavy FL sizing, or not. Your choice.

Die makers base dimensions from SAAMI min. If your chamber is not at SAAMI min, then you'll likely end up with excess sizing from their dies. As far a -3thou being a goal,, that would be a pretty bad goal.
Would it surprise me? NO
Reloading tool makers are not the experts in reloading, or shooting tiny groups, or dropping game with single shots. WE ARE. We determine what works and what doesn't. We establish the standards and drive the markets.
As a reloader, hunter, competitor, you control everything. It is all YOUR choices.

 

[cohunt]

I read an article onece where a guy tested neck tension in regards to accuracy..he originally tested 2 guns (each a different caliber--one was a 30 and iirc the other one was a 243 or 25 cal)

he did neck turn--he started with ONE known variable and everything else in each caliber was the same so he was only testing neck tension--he started with a known accurate load and used .001" neck tension, then tested .002", the .003" all the way up to .006"--- he noted that one rifle liked .001" the other liked .003-- but both shot well with .002 also---from there his conclusions on the .004-.006" neck tension were that in both rifles the accuracy decreased (got worse) as the neck tension increased --he noted that the .004 was worse in both rifles, he also noticed that the .005 was worse than the .004 and the .006 was worse than the .005

from this small test sample he noted that from .001-.003" was the "sweet spot" for accuracy-- but he also noted that at a further date/test with a semi auto---anything less than .003" was causing bullet set back in the semi-auto magazine..

His conclusion was for semi auto .003" was the perfect neck tension but for bolt rifle he was willing to go as light as .001" but watched for bullet set back in larger calibers.



Take it for what it's worth, but his testing methods seem good to me--just a small test sample of 3 guns in 3 different calibers

 

[bigedp51]

I just read that David Tubb is using .004 neck tension with his tube gun.

And neck spring back is governed by brass hardness and annealing.

Below .003 neck tension for a .223

Neck Tension — Not Just Bushing Size
http://www.accurateshooter.com/technical-articles/reloading/neck-tension-not-just-bushing-size/

Reloading Tip: How to Set Optimal Case Neck Tension
http://bulletin.accurateshooter.com/2017/10/reloading-tip-how-to-set-optimal-case-neck-tension/