Seeking a good source for expanding mandrels

[Alex Wheeler]

Your going to have to do your own testing in your rifle. Theres no answer for your questions. All combos will react differently. I have seen a .001" bushing change destroy a load. In other cases the changes are small.

Seating force is not neck tension. They correlate slightly. Seating force is more a measurement of friction. I personally would not use seating force as a measurement of how much grip on the bullet you have, and grip is what shows on target IMO.

 

[dmoran]

@kvd
Best way to find out is to test your own scenario's in your own rifles, letting the targets be the proof.
My own experience and short reply is: neck tension effects accuracy (some times considerably).
Donovan

 

[kvd]

Your going to have to do your own testing in your rifle. Theres no answer for your questions. All combos will react differently. I have seen a .001" bushing change destroy a load. In other cases the changes are small.

Seating force is not neck tension. They correlate slightly. Seating force is more a measurement of friction. I personally would not use seating force as a measurement of how much grip on the bullet you have, and grip is what shows on target IMO.

I agree that seating force is not neck tension. I actually do not believe it is possible for the thin, annealed, neck of a brass case to exert any tension at all - at least not as I understand the concept of say a freeze fit bushing or bearing that generates a radial compression on the bushing and a tangential tension in the housing. Seems seating force as measured with the 21st century tool is the only force measurement available so it gets quoted as neck tension. At least the units are right.

@kvd
Best way to find out is to test your own scenario's in your own rifles, letting the targets be the proof.
My own experience and short reply is: neck tension effects accuracy (some times considerably).
Donovan

I can see your point but what am I testing? What are miniscule changes in "clasp" of the bullet by the case neck effecting? Possibly it is not known why playing with the neck size before seating a bullet makes a difference in accuracy. I guess just do it and see what happens is the best answer at this juncture.

Thank you for the responses.

Ken

 

[bigbulls]

Darrel Holland makes a nice set. Holland gun smithing

 

[Tiratore]

This is a one-dimensional analysis showing the calculation of force needed to get the bullet moving out of the case. For this condition, the sizing of the neck is such that seating the bullet causes the neck to yield. This is the maximum force that can be produced. Brass yield strength can vary quite a lot, and this is one reason some are looking at regular annealing, which will both lower yield strength and make it more uniform from case to case.

 

[Alex Wheeler]

View attachment 1010957
This is a one-dimensional analysis showing the calculation of force needed to get the bullet moving out of the case. For this condition, the sizing of the neck is such that seating the bullet causes the neck to yield. This is the maximum force that can be produced. Brass yield strength can vary quite a lot, and this is one reason some are looking at regular annealing, which will both lower yield strength and make it more uniform from case to case.

Since I dont know the definitions of the letters and am certainly no math wiz, can you solve this with a .2" long neck and a .0107 thickness? Does this take into account bullet weight? How much does it change annealed vs annealed? I know that you can anneal to many different levels, but on average.
Thanks

 

[Tiratore]

The perfectly elastic, perfectly plastic model of material behavior used here is a poor one for determining seating force exactly, but it is instructive. Basically, there is a rather small window where the amount of sizing greatly affects the force needed to move the bullet either way.

That said, we have seen an effect on group size when seating engagement and neck sizing have been changed. We're just having trouble explaining "why."

 

[Tiratore]

Since I dont know the definitions of the letters and am certainly no math wiz, can you solve this with a .2" long neck and a .0107 thickness? Does this take into account bullet weight? How much does it change annealed vs annealed? I know that you can anneal to many different levels, but on average.
Thanks

Tell me the caliber and neck ID before the bullet is seated.

 

[Alex Wheeler]

6mm, .238"

 

[Tiratore]

6mm, .238"

OK, the calculation only accounts for neck tension, so bullet mass doesn't enter into the calculation. The bullet is assumed to be rigid. Brass, according to the on-line handbook I just consulted, can have yield strengths between 11 ksi and 65 ksi, depending on work hardening and annealing history. So, the force needed to seat, or unseat, a bullet as you described can vary between 29 lb and 175 lb, depending on how hard the piece of brass is. Maybe someone can help us out with a nominal value for brass yield strength ... I'd only be guessing. So this says the bullet moves when the chamber pressure is between 625 psi and 3770 psi, depending on the hardness of the brass in the neck.

Somebody please check my math. I may have had another senior moment. It wouldn't be the first time.

 

[Alex Wheeler]

Interesting. There is definitely something left out. We know the neck expands before or during bullet movement. If the bullet slides out of the neck the necks would not expand to the chamber. Thats something thats probably impossible to calculate. And what coefficient of friction are you using between bullet and neck to come up with the seating force? Reason I ask is, friction doesnt seen to show on target but tension/interference does.

 

[hrlincoln]

Possibly it is not known why playing with the neck size before seating a bullet makes a difference in accuracy. I guess just do it and see what happens is the best answer at this juncture.

From the tech article section....

http://www.accurateshooter.com/technical-articles/reloading/neck-tension-not-just-bushing-size/

 

[Steve Jennings]

Steve, both you & Alex would have to qualify your arguments(narrow them down), for any credible considerations.
The 'most consistent and straightest' at -4thou fails tests w/resp to my necks having -1thou interference fit for ~.200" length against bullet bearing seated ~.300" deep. It would do nothing for straightness, nor consistency. Truly, -4thou would do no more than overwork necks for my situation. So whatever your stating, it needs to be qualified to the specific situation it applys to.

Alex, you didn't seem to understand that excess interference fit is not tension directly(or possibly at all), and only contributes while sizing greater length than seated bearing. So to suggest differing interference fit changes tune, you should narrow it to the actual situation in which this might occur(not broadly). Like with Steve's implications, yours in no way applies to my partial neck sizing situation(which is not uncommon).

I agree and know for myself that tension affects tune, but everybody does not FL size necks, and seating forces(friction/interference fits) are not tension, or even contributing in some cases. Add annealing, neck thickness, sizing process, and there are too many possible situations to hang one hat on.

Mike, What caused us to have a look at the ID of necks was shadows that looked like uneven wear or ?? So, we measured the ID at .050" vertical increments and observed that the neck ID wore or bent or burned out ( ? ) to produce a coke bottle or irregular shape after firing. We found that it was possible to return the neck ID to almost straight and round as mentioned. A bushing only makes the OD of the neck round and on size. I would bet half a six pack that your group size would decrease slightly if your cases were finish sized with some sort of ID expander.

 

[kvd]

From the tech article section....

http://www.accurateshooter.com/technical-articles/reloading/neck-tension-not-just-bushing-size/

Thank you for the link. I guess what it comes down to for me and what hasn't been explained is - how can the few hundred psi or even a few thousand psi required to initially push the bullet free of the case neck possible be of any importance compared to the 50,000 + psi pressure generated in the chamber. Think of the small force involved in pulling a bullet from a case versus the effort that would be required to push one down the barrel. How does this small initial force early on in the combustion of the powder charge followed by a much greater force show up on target?

OK, the calculation only accounts for neck tension, so bullet mass doesn't enter into the calculation. The bullet is assumed to be rigid. Brass, according to the on-line handbook I just consulted, can have yield strengths between 11 ksi and 65 ksi, depending on work hardening and annealing history. So, the force needed to seat, or unseat, a bullet as you described can vary between 29 lb and 175 lb, depending on how hard the piece of brass is. Maybe someone can help us out with a nominal value for brass yield strength ... I'd only be guessing. So this says the bullet moves when the chamber pressure is between 625 psi and 3770 psi, depending on the hardness of the brass in the neck.

Somebody please check my math. I may have had another senior moment. It wouldn't be the first time.

For me, where the whole thing goes out the window, is that we really don't know what tension comes from the interference fit of a billet in a case neck. Just to many variables. You must be a Stress Engineer or at least familiar with metallurgy.

Ken

 

[kvd]

Mike, What caused us to have a look at the ID of necks was shadows that looked like uneven wear or ?? So, we measured the ID at .050" vertical increments and observed that the neck ID wore or bent or burned out ( ? ) to produce a coke bottle or irregular shape after firing. We found that it was possible to return the neck ID to almost straight and round as mentioned. A bushing only makes the OD of the neck round and on size. I would bet half a six pack that your group size would decrease slightly if your cases were finish sized with some sort of ID expander.

Possibly galvanic corrosion? Normally brass and copper are a decent galvanic couple but it should be noted that the more cathodic brass would be the much greater surface area in the copper clad bullet/ brass case neck couple and the general rule is that the more noble or anodic metal area should be greater. Add to this the fact that the last contact on the bullet may that been sweaty fingers and one can readily see the conditions for galvanic corrosion to set in fairly quickly. People do routinely report bullets sticking in cases that require considerable force to remove - blaming the problem on "cold welding". This is why I think seating the bullets to final depth just before shooting them is a good practice.

Ken

 

[Tiratore]

Interesting. There is definitely something left out. We know the neck expands before or during bullet movement. If the bullet slides out of the neck the necks would not expand to the chamber. Thats something thats probably impossible to calculate. And what coefficient of friction are you using between bullet and neck to come up with the seating force? Reason I ask is, friction doesnt seen to show on target but tension/interference does.

I used 0.2 for coefficient of friction ... looked up copper-on-brass. That opens up a whole new set of variables. What about carbon deposits? Oxidation (or whatever) on the brass? I've gone to brushing case ID, and running necks around a tin with graphite and number nine shot ... at least when loading at home rather than at the range.

And why would a response to a several hundred psi affect anything in an environment with such a violent release of energy? And waves travel more than ten times faster in brass than in propellant gas, so does the grip on the bullet release before the bullet moves? Lots of mysteries here. I'm sure someone who works in the industry may know the answers.

 

[dmoran]

@Tiratore
Even if we came up with all the data inputs needed accurately for a given case for probable mathematics , all would change after the case was fired and on a different cycle. Bullet release in the combustion cycle is one of those internal ballistic aspects that is not totally known, and where theories are more known then reality.
Just to many effecting aspects for certainty.
Donovan

 

[kvd]

I guess I shouldn't be surprised that this is one more example of the fact that we humans possess very little exact knowledge about anything. Precision reloading is not a black art but in my mind, there is still much to understand before the science is fully understood.
That being said, I'm awaiting a 0.001 inch smaller bushing to tighten up the neck a tad more. I may not know why exactly, but if I can shoot smaller group closer to where I'm aiming - why not!

Happy shooting all.

Ken

 

[Alex Wheeler]

I am sure this would be a very easy thing for a lab to figure out. But like a lot of things someone is going to have to pay for that testing. Its just not important enough for anyone to foot the bill. As shooters we just need to know that it does matter, even if it shouldnt. Simple testing will tell you the correct amount of neck tension as well as any neck id prep you want to try. That is the part thats supposed to be the fun part. If someone could tell me the exact load for my rifle every time that would take the fun right out of it.

 

[Joe R]

Good stuff guys, lots to think about.

Tiratore (doesn't that mean Shooter? ) you've made a real contribution to my understanding of neck tension. You've given me a few things to think about, but you also incidentally made the best case I've seen for annealing after each firing.

Kindest regards,

Joe