Bushing Size for Mandrel

[Kraven]

When you use a mandrel to expand the neck, how much smaller bushing do you use for an ideal uniform expansion? Is 0.001” under enough?

 

[dgeesaman]

I asked this question a few months ago and the consensus is that’s on the light side. .002 to .001 is the popular range. Around .001 it might not resize the brass at all and you need to be annealing each load.

David

 

[Uncle Ed]

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

"The easiest way to determine the proper diameter bushing is to measure the neck diameter of several loaded or dummy cartridges with an accurate micrometer. (These dummy cartridges can be loaded with your old set of dies or a borrowed set.) Then, simply subtract 0.001" from the cartridge that had the smallest average measurement. This will allow for a slight amount of spring back and create a proper press fit for the bullet.

The above methods of determining bushing size require that the cases being sized have a fairly uniform neck wall thickness or have been neck turned. 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".

 

[Kraven]

Hi Uncle Ed,

I understand the bushing selection part. I was just wondering if there is a guide on how much smaller the neck needs to be for the mandrel to be effective in uniforming the inside of the neck. My final neck tension is by using a turning mandrel which gives me 0.002” neck tension on bullets. If I use a 0.002” bushing with a turning mandrel, also 0.002”, I just glides in and out with very little effort. Not sure if its ideal.

 

[mikecr]

Ideally, for un-turned necks, you would choose a bushing to provide interference of ~1-1.5 under cal(after springback). Then run an at cal mandrel through for expansion. This is essentially a pre-seating action, in that you're no longer using bullets for expander buttons, but letting a hardened mandrel do it. Any expansion of ~3/4thou causes yielding, which is moving brass(incl donut) outward. When you remove the mandrel, the neck springs back inward to ~1/2thou interference. The force behind that springback X the area gripped, is your tension. So you would adjust bushing sizing LENGTH to adjust neck tension, and ensuring that length never exceeds seated bullet bearing.

If you're using the Sinclair/PMA system or 21st Century, there are a few options for getting best mandrels sizing. Too bad they're not all carbide..
http://www.xxicsi.com/caliber-specific-expander-mandrels.html
There are also pin gage systems. But they don't look optimally shaped for this operation.

 

[Uncle Ed]

Hi Uncle Ed,

I understand the bushing selection part. I was just wondering if there is a guide on how much smaller the neck needs to be for the mandrel to be effective in uniforming the inside of the neck. My final neck tension is by using a turning mandrel which gives me 0.002” neck tension on bullets. If I use a 0.002” bushing with a turning mandrel, also 0.002”, I just glides in and out with very little effort. Not sure if its ideal.

If the necks are not turned the mandril needs to push the neck thickness variations to the outside of the neck.

I would think the bushing would need to be small enough in diameter to allow the mandrel to make the inside of the neck concentric.

I have seen Remington .223 cases with .009 neck thickness variations and would never think of using a bushing die on cases this bad.

The Redding bushing FAQ tells you to make the necks "a couple of thousandths smaller" on unturned necks. And I would interpret this as using a bushing .002 or .003 smaller than if sizing a turned neck.

Bottom line, Redding puts a expander in their bushing dies for a reason. And your answer would be how many thousandths does your necks vary when selecting a bushing.

 

[mikecr]

No, bushing selection has nothing to do with thickness variance or whether necks are turned or not.
It is loaded neck diameter minus a couple thou, with adjustment often needed because of varying neck clearances. The higher the clearance the greater sizing ANGLE will be & brass rolls with angles to cause more sizing than stamped on bushings. For Reading, this adjustment point is usually 5thou+ of needed downsizing.

Example:
You have loaded neck diameters of .2900" and chamber neck clearance of .006".
You choose a bushing stamped .288
Your fired necks measure .2955"
You expect the neck to size down to .2880 and spring back to ~.2885, leaving .0015" interference, but instead it sizes down to .2875, springing back to .2880. It might size even more..
This happened because the bushing sizing angle is high(technically, beyond design).

There is also a sizing personality in play. Lapua brown box 223Rem does not size the same as Norma 300WSM. Different [thickness per loop diameter], and different brass alloys. Add your annealing to the abstract as well..

 

[Uncle Ed]

No, bushing selection has nothing to do with thickness variance or whether necks are turned or not.

Who do we believe, mikecr or the Redding bushing FAQ. The Redding bushing FAQ specifically tells you to use a smaller bushing if the neck thickness varies .002 or more and use the dies expander.

So why use the bullet as a expander to push the thickness variations to the outside of the neck?

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".

 

[mikecr]

Necks only spring back ~1/2thou.
Any sizing beyond this is yielding. So if you were using the correct size MANDREL (at cal), expanding 1.5thou interference, you would push reasonable thickness variance (~1thou) outward to stay.

For 2thou of variance, which I've never seen: IT IS NOT NORMAL
Even neck turning would not be in order for brass that broken.
And I would not depart from sound reloading for anomalies.
But, I will concede that Redding is right about that kind of situation. And maybe they mentioned a need at that point for constant annealing, including during load development.

Thanks Uncle Ed

 

[Uncle Ed]

Even Redding can't make up their minds.

Tech Line & Tips (FAQs)
Concentricity & Bushing Dies
https://www.redding-reloading.com/tech-line-a-tips-faqs/142-concentricity-a-bushing-dies

"From tests we have conducted, we have learned that selecting the correct bushing is the most important factor in producing sized case necks that have good concentricity with the case body. Our tests showed that case neck concentricity is directly proportional to bushing size. In other words, as you size case necks with progressively smaller bushings, the concentricity gets progressively worse.

Our current recommendation, is to select a bushing that is .001 to .002" smaller than the loaded cartridge neck diameter. For example, if the neck diameter of your loaded cartridges is .248", start with a .247 or .246" bushing. We've had to change our initial recommendation, because some of cartridge cases manufactured today have neck walls near the minimum SAAMI thickness. When using brass which is at the thinner end of the SAAMI spec. we have found the bushing which is .001" smaller will provide the best result.

To create precision reloads, you must start with cases of good quality. They should all be from the same manufacturer and lot number. A good measure of case quality is how uniform the neck wall thickness is. Cases with uniform neck wall thickness, will be of uniform thickness all the way to the base. This is important for accuracy, as the cases will expand uniformly upon firing, and contract uniformly when sized. Neck turning helps, but it's only a partial cure, as you can't turn the case wall all the way to the base. The Redding Case Neck Gauge is the preferred instrument for checking neck wall thickness and uniformity. Also note that the concentricity of a fired case only indicates how concentric your firearm's chamber is. It provides you with little or no information on the quality of the cases you're using".

My comments, so from the above recommendation and if the neck thickness varies .002 or more you could end up with a bushing .004 to .005 "smaller" than the loaded neck diameter and then use the expander. Don't shoot the messenger.

 

[David Christian]

Even Redding can't make up their minds.

Tech Line & Tips (FAQs)
Concentricity & Bushing Dies
https://www.redding-reloading.com/tech-line-a-tips-faqs/142-concentricity-a-bushing-dies

"From tests we have conducted, we have learned that selecting the correct bushing is the most important factor in producing sized case necks that have good concentricity with the case body. Our tests showed that case neck concentricity is directly proportional to bushing size. In other words, as you size case necks with progressively smaller bushings, the concentricity gets progressively worse.

Our current recommendation, is to select a bushing that is .001 to .002" smaller than the loaded cartridge neck diameter. For example, if the neck diameter of your loaded cartridges is .248", start with a .247 or .246" bushing. We've had to change our initial recommendation, because some of cartridge cases manufactured today have neck walls near the minimum SAAMI thickness. When using brass which is at the thinner end of the SAAMI spec. we have found the bushing which is .001" smaller will provide the best result.

To create precision reloads, you must start with cases of good quality. They should all be from the same manufacturer and lot number. A good measure of case quality is how uniform the neck wall thickness is. Cases with uniform neck wall thickness, will be of uniform thickness all the way to the base. This is important for accuracy, as the cases will expand uniformly upon firing, and contract uniformly when sized. Neck turning helps, but it's only a partial cure, as you can't turn the case wall all the way to the base. The Redding Case Neck Gauge is the preferred instrument for checking neck wall thickness and uniformity. Also note that the concentricity of a fired case only indicates how concentric your firearm's chamber is. It provides you with little or no information on the quality of the cases you're using".

My comments, so from the above recommendation and if the neck thickness varies .002 or more you could end up with a bushing .004 to .005 "smaller" than the loaded neck diameter and then use the expander. Don't shoot the messenger.

IMHO, this thread has moved in two different directions based upon one’s desire for accuracy. @Uncle Ed, all of your posts are spot on for the average shooter plinking rounds, and that is exactly who Redding is speaking to. @mikecr, is dead on for achieving the greatest precision in neck tension for the most discerning shooters. Those loading for precision would not even think of loading brass with extreme neck wall thicknesses (.002), nor would they want to oversize cases more than needed with a too small of bushing.

As stated earlier, a mandrel or gage pin matched with the appropriate sized bushing should be used in combination to produce the best results.

 

[David Christian]

As an aside, a shooting buddy just did a micro test loading identical rounds (brass, powder, bullets, seating depth) with his .284 Shehane but varied using an expander ball versus a pin gage. He fired them blind alternating 5 shots at a time—40 rounds total. Again, this is a micro test, but a start. Consistency of the pin gage seems to win.

 

[INTJ]

I believe @mikecr for precision. Using the K&M Primer Gauge he recommended cut the ES on my LR BR 6 BRA from teens to single digits for tuned loads.

I use a bushing and an expander in my Whidden dies. I am getting 20 PSI with about a +/- 2 PSI variation seating pressure of my 21st Century Hydro Seater. Here are my numbers:

Fired case = .266 (reamer cuts a .267 neck)
Bushing = .260
Expander = .239
Neck Wall = .0115
Sized case = .261
Loaded round = .2645

So the bushing takes it to .260, the expander to .262 and .001" of spring back yields .261.

I wouldn't argue that I have .0005" error in my measurements. Mitituyo digital caliper (a real one). I know that .0035" of neck tension seems like a lot, but 20 PSI is not heavy seating pressure, and it super consistent. I anneal after every firing.

 

[billslatteryjr]

As an aside, a shooting buddy just did a micro test loading identical rounds (brass, powder, bullets, seating depth) with his .284 Shehane but varied using an expander ball versus a pin gage. He fired them blind alternating 5 shots at a time—40 rounds total. Again, this is a micro test, but a start. Consistency of the pin gage seems to win.
View attachment 1186376

Sure would like to see the same test done with pin gauge vs just using a bushing that gives the same inside neck diameter on turned necks. Wonder how much difference using the bullet to push a turned neck's small thickness difference(what .0005 or less?) to the outside vs having that slight difference on the outside causing a slight uneven resistance to the expansion to begin with?

 

[Uncle Ed]

IMHO, this thread has moved in two different directions based upon one’s desire for accuracy. [B][COLOR=#ff0000]@Uncle Ed[/COLOR][/B], all of your posts are spot on for the average shooter plinking rounds, and that is exactly who Redding is speaking to. @mikecr, is dead on for achieving the greatest precision in neck tension for the most discerning shooters. Those loading for precision would not even think of loading brass with extreme neck wall thicknesses (.002), nor would they want to oversize cases more than needed with a too small of bushing.

As stated earlier, a mandrel or gage pin matched with the appropriate sized bushing should be used in combination to produce the best results.

I do not believe that any "average shooter" would buy a bushing die and bushings for loading plinking rounds in any type rifle.

And the OP did not say what type or make rifle he is loading for or if he is just hunting or shooting in competition.

So the OP should tell us if he is an "average shooter" with an average off the shelf factory rifle with a Tasco scope.

Bottom line, if the OP was an above average competitive shooter he would not have asked the question that is the subject of this posting.

P.S. Even my average rifles are good enough for head shots on Zombies.

 

[Dusty Stevens]

P.S. Even my average rifles are good enough for head shots on Zombies.

What distance? I see you post alot about a 303 british

 

[Uncle Ed]

What distance? I see you post alot about a 303 british

What distance do you shoot Zombies at Dusty Stevens.

 

[Dusty Stevens]

What distance do you shoot Zombies at Dusty Stevens.

1 mile. They stank

 

[Uncle Ed]

With all due respect to the competitive shooters in this forum, there are reloaders here that do not shoot in any form of competitive shooting. And they are looking for answers to make more accurate ammunition that will never be used in competition.

The OP has made 2 posts here and asked a question about bushing dies, expander mandrils, and neck tension.

Here is what we do not know about the OP, what type rifle is he reloading for, what brand brass he is using, and his neck thickness variations.

My impression of the OP question was he was asking why his turning mandril "just glides in and out with very little effort." We do not know his neck thickness, how many times the case has been fired, and the amount of spring back after sizing.

The OP is using a bushing .002 smaller than a loaded round and a turning mandril .002 smaller than bullet diameter. And his question is should the turning mandril be just gliding in and out with very little effort."

 

[Dusty Stevens]

With all due respect to the competitive shooters in this forum, there are reloaders here that do not shoot in any form of competitive shooting. And they are looking for answers to make more accurate ammunition that will never be used in competition.

The OP has made 2 posts here and asked a question about bushing dies, expander mandrils, and neck tension.

Here is what we do not know about the OP, what type rifle is he reloading for, what brand brass he is using, and his neck thickness variations.

My impression of the OP question was he was asking why his turning mandril "just glides in and out with very little effort." We do not know his neck thickness, how many times the case has been fired, and the amount of spring back after sizing.

The OP is using a bushing .002 smaller than a loaded round and a turning mandril .002 smaller than bullet diameter. And his question is should the turning mandril be just gliding in and out with very little effort."

No if he sizes it down .002 it will expand at least .001 which makes that .001 too big if im reading it right. Gonna have to tighten it way up then let the expander mandrel set it right for the turning mandrel