To bush or mandrel

[Lonewolf74]

I'm not positive if what you and I are saying is the same or not.

What I believe Mikecr is saying is that your neck tension will never be greater then the spring back of your brass. Weather you size your neck .001 or .010 under bullet diameter your tension is still going to be about .001 or the spring back value of your brass. The only thing your accomplishing by sizing under more then .001 is increasing seating force and expanding the neck with the bullet and possibly shaving material off the bullet jacket, because the bullet will resize (expand) the neck to it's diameter

The only way to manipulate the "hold" on the bullet is to increase or decrease the length of the neck that is sized which will increase or decrease the interference of the bullet bearing and case neck surfaces.

Maybe Mikecr will clarify if I'm off on any points?

 

[Mike Matteson]

Kind of on the same thing, but I am building a 6mm-280AI wildcat rifle. Getting 280AI brass from Peterson, when they are available and in a 500 lot, so I won't run out brass for my life time. I am having a reduced the neck dia. 1. I can cut the necks to thickness at the 280AI caliber first then size them down to 6mm. OR 2. I can size down to the 6mm and then cut the necks for thickness. What I see is sizing down the spring back as a possible problem. So I would think that using a mandrel that would get ID to. .243 after spring back would be first, and then cut the neck for thickness. That's the way I am leaning towards. This the first time I am using a tighten chamber in rifle. All the others rifles I had built have been standard chambers dimensions.

 

[Mikecr]

Mike, you'll be better to turn necks at NEW-NATIVE cal. With this you get best turning mandrel fit, and you won't need to turn onto neck-shoulder junction, as sizing down to 24cal will put some of the turned neck into new shoulder. Just turn full length of 28cal necks and size down to 24cal.
This is will be trial & error, so work into desired with cases culled for issues (like thickness variance). Should only take a few.

Lonewolf74, your thinking is same as mine. I really wish we had a way to measure this tension, which is really hoop tension.
I do know it's way more complicated than simple interference assumptions.
You have:
Where your putting yourself on the specific brass alloy stress-strain curve
The granular structure at any given reloading cycle
The diameter/area of the hoop
The length/area of sized, springing back against seated bullet bearing
The shoulder angle resisting through at least the donut area of neck length
The thickness of necks

I'll add, the biggest misunderstanding folks latch onto is a notion of 'pull force'. That tension is somehow friction.
It is not, and easy enough to prove it is not, so those people are truly lost in this.
Our bullets are released and swinging in the wind, as pressure X area of the charge expands neck/shoulder but a relative few molecules worth of clearance. It takes only a tiny portion of pressure peak to do this -very quickly.
Understanding this will lead you to see and use neck tension as a FINE tuning adjustment.
If needing extremes here to reach a 'good' load, then it's not such a good load. The bullet/cartridge/load is wrong somewhere.
A normal spring back force X area gripping is plenty of adjustment.

 

[FrogFire7]

I use a mandrel as the final step in my reloading process

I'd use it as one of the first steps, but that's just me

I kid, I kid

 

[Mike Matteson]

I want to Thank You both for the input. I have type it down on my 6mm built information. I first though it would be better to turn the necks in an unfired state, then reversed my thinking, and now reversed it again. I was concern about the donut. I have just purchase a 21st century neck turning system with cutting set up for each caliber I load for. The 284 dia. was one of them. Most all of my new reloading equipment is being sent to my son place in Montana. I setting up to move here shortly. Mandrel I will get when I get there.

 

[Mikecr]

You don't get donut formation from downsizing. Only upsizing.

 

[Mike Matteson]

I understand that from the other info you have supplied. Which is a good thing.

 

[ScottB338]

These technical discussions are what make reloading and this forum so much fun!

Has anyone experimented with pulling bullets from assembled rounds to try and determine what "spring back" forces are involved over time with holding the bullet. By that, I mean does anyone know how much spring back tension is possible with any given neck diameter and/or case wall thickness for holding a bullet?

If, say, for example, has it been determined that a neck that is .005" undersize diameter of a
bullet, can only provide .002" of actual neck grip because part of that additional diameter reduction is lost to the brass yielding beyond spring back when the bullet is seated?

...maybe I should put the question on its own thread...instead of hijacking this one. Sorry OP.

 

[Mike Matteson]

Not a problem, but no pulling bullets, and spring back.