Bushing Die sizing vs Mandrel Die sizing ?

[foxguy]

A Bushing Die Vs a Mandrel Die.

I know this is all dependent on the hardness of the brass. lets just say once fired Brass and the brass is regularly annealed to retain elasticity.

In this example I am thinking Laupa 6mm Brass .0135 Wall thickness - No turn chamber/neck.

When sizing with a Bushing Die, the bushing squeeze's the OD of the neck to a reduced diameter and then springs back to a slightly larger diameter. if you want a .267 diameter neck you use a .267 diameter bushing.

When using a Mandrel die, it enlarges the ID of the neck and springs back to a slightly smaller ID

Example:
If you want to use a mandrel die to enlarge the neck say to a .267 OD / .242 ID what size Mandrel would be required. a little more thought, a Neck sizing Die has to be used first to reduce the necks size ( I suspect .0005-.001 undersize the finished size) and then the Mandrel Die to open the ID back up to the finished size desired.

IE....
Is there a general rule for a Mandrels over size in thousands in order to achieve the ID one wants the finished neck size to be?

All the talk about sizing with a Mandrel has me wondering, as the sizing is going in the opposite direction. I have to believe the members on this site have already checked this out and have a pretty good idea on how this mandrel sizing works out.

Thanks

edit: a little more information...

My rifle 6MM BR- Fired case OD neck diameter .2695-.270
Loaded round OD neck diameter .268
I have been using a neck bushing - sizing .267(finished OD size .2665-.267)

 

[Sheldon N]

Here's the results I'm getting, if it's of any assistance.

6 Dasher fireformed Lapua brass
No turn chamber, .2725 OD fired case at the neck
OD of loaded round at the neck is .2675
Sizing down with a FL die with a .265 neck (Forster FL die with custom honed neck, no expander ball)
Mandrel is a Sinclair carbide turning mandrel .241 diameter

After FL sizing the neck comes out at .2650. After running over the mandrel the neck OD measures .2655. I anneal every firing before sizing and am not seeing much in the way of springback from either the FL die or the mandrel. I did have a bushing die before the Forster, but I've found the Forster to produce less runout.

 

[Bart B.]

Now you know why Forster's one piece FL die make straighter cases. Two piece die body's bushing has 1 to 2 thousandths radial slop in the die bushing recess. Bushings are that much smaller than the die recess they go in. No slop in one piece die's neck; it's always perfectly aligned to the die case body sizing chamber.

 

[fguffey]

When using a Mandrel die, it enlarges the ID of the neck and springs back to a slightly smaller ID

All of my primer punch/expander plug assembles get involved after the neck is sized down by the sizer die, when the ram is lowered the expander plug is pulled thorough the neck. Reloaders that are not in mortal combat with reloading understand when the sizer plug resist being pulled through the neck when the ram is lowered it is time to reduce the diameter of the plug or anneal or thin the neck etc.. I have sized cases that required the sizer plug to make 3 squeaks before making its exit from the neck.

What should it feel like when puling the plug through the neck? My favorite cases are new and once fired, and then there are my most favorite cases; my most favorite cases are cases that have been fired in trashy Ol' large chambers, something like machine gun chambers. Manufacturers do not make cases for me, all of the cases made for reloaders are made for other reloaders, they are the ones that fire to form, I had rather let someone else fire the case. I had rather form the case to fit, it is not easy to form a case that is too small for the chamber.

F. Guffey

 

[Bart B.]

When sizing with a Bushing Die, the bushing squeeze's the OD of the neck to a reduced diameter and then springs back to a slightly larger diameter. if you want a .267 diameter neck you use a .267 diameter bushing.

All of my 30 caliber case necks spring back out about .001" larger in diameter than the die's neck diameter.

Why wouldn't 24 caliber stuff not be about the same?

Aren't all bushing neck diameter size numbers their exact dimension?

 

[JRS]

All of my 30 caliber case necks spring back out about .001" larger in diameter than the die's neck diameter.

Why wouldn't 24 caliber stuff not be about the same?

Aren't all bushing neck diameter size numbers their exact dimension?

If you want bushings that closely resemble "exact", you need to call Alan Warner and order one of his sizing dies

 

[Bart B.]

I've used hole micrometers measuring RCBS, Jones and Redding bushings. All are within a couple tenths of the ID number stamped size on them. So are Warner's stuff.