Expander Mandrel Confusion

[Beetys]

Hey guys,

I'm very slow.

I'm loading 6.5 creedmoor, and I have a 0.263 expander mandrel.

However, when I run the brass (Lapua) through the mandrel, and measure neck outside diameter, i'm getting 0.2895.

Can someone explain to me what I'm missing?

I was thinking my neck outside diameter was going to be 0.293 (0.263 + (0.015 x 2)) for 0.001 neck tension.

Thank you!!

 

[Straightshooter1]

Hey guys,

I'm very slow.

I'm loading 6.5 creedmoor, and I have a 0.263 expander mandrel.

However, when I run the brass (Lapua) through the mandrel, and measure neck outside diameter, i'm getting 0.2895.

Can someone explain to me what I'm missing?

I was thinking my neck outside diameter was going to be 0.293 (0.263 + (0.015 x 2)) for 0.001 neck tension.

Thank you!!

After running that expander mandrel, there's going to be some springback, which can vary depending on the hardness of your brass.

Also, are you sure the neck thickness is .015 . . . or could it be .0145? You won't know for sure unless you actually measure the neck thickness with a micrometer.

 

[Beetys]

Ok gotcha, thanks.

Would annealing reduce spring back?

And im assuming you guys have multiple mandrels and bushings for any particular cartridge? Is that standard?

 

[jepp2]

And im assuming you guys have multiple mandrels and bushings for any particular cartridge? Is that standard?

21'st Century sells the mandrels in 0.0005" increments if that gives you a hint. My experience was that I just needed 1 more mandrel and 1 more sizing bushing to be perfect. Kind of like free beer tomorrow except you never get to tomorrow.

When you measure you case neck thickness, you can't use calipers and it takes a special micrometer (tubing).

 

[RegionRat]

When you measure you case neck thickness, you can't use calipers and it takes a special micrometer (tubing).

True for the most part, but if you have a neck with decent typical neck tension loaded over a known bullet, the measurement over the loaded neck has the known value of the bullet on the inside and most micrometer calipers are good for the outside. Both types of readings are good to know, the tube mic as well as the over the bullet value. YMMV

 

[Laurie]

im assuming you guys have multiple mandrels and bushings for any particular cartridge?

Some do.

Is that standard?

No.

The Sinclair / Brownells 'E' mandrels are c. 0.001" under nominal bullet diameters, and they've worked fine for me in all calibres from .20 to .30. People get a bit of a fetish about neck tension, but I've long been of the view that providing there is enough of it, consistency is more important than small changes in amounts, so you're seeking nodes at one particular value.

Re the amount of tension you have, you now need to measure a bullet's shank diameter (they can easily vary by 0.0005" between makes, occasionally a full thou'), then seat a bullet and remeasure the neck O/D. By simple arithmetic you get both total neck thickness and a value for 'tension'.

 

[Beetys]

21'st Century sells the mandrels in 0.0005" increments if that gives you a hint. My experience was that I just needed 1 more mandrel and 1 more sizing bushing to be perfect. Kind of like free beer tomorrow except you never get to tomorrow.

When you measure you case neck thickness, you can't use calipers and it takes a special micrometer (tubing).

Ok thanks.

how did you determine choosing that second second mandrel? Based on the amount of kick back that I’m getting on my brass?

 

[RegionRat]

Would annealing reduce spring back?

And im assuming you guys have multiple mandrels and bushings for any particular cartridge? Is that standard?

Yes, the purpose of annealing is to reduce work hardening, and that reduces the "spring back".

Most of us who use an expander mandrel do use very fine steps to control the results, and we are ready with sizes above and below for contingencies. That way, we are not stopped waiting for tools.

 

[jepp2]

how did you determine choosing that second second mandrel?

I usually calculate the one I think I will need and get two more, one +0.0005 and one -0.0005. But as mentioned since I also turn case necks (and that will change the sizing bushings you need to use) I have expander and turning mandrels.

 

[Beetys]

Some do.

No.

The Sinclair / Brownells 'E' mandrels are c. 0.001" under nominal bullet diameters, and they've worked fine for me in all calibres from .20 to .30. People get a bit of a fetish about neck tension, but I've long been of the view that providing there is enough of it, consistency is more important than small changes in amounts, so you're seeking nodes at one particular value.

Re the amount of tension you have, you now need to measure a bullet's shank diameter (they can easily vary by 0.0005" between makes, occasionally a full thou'), then seat a bullet and remeasure the neck O/D. By simple arithmetic you get both total neck thickness and a value for 'tension'.

Thanks. In your experience, do you see muzzle velocity fluctuation with varying neck tensions?

edit: I guess my question is… is there a node for neck tension?

 

[RegionRat]

Thanks. In your experience, do you see muzzle velocity fluctuation with varying neck tensions?

edit: I guess my question is… is there a node for neck tension?

Yes, neck tension is important and has to be coordinated with your style of bullets and seating.

For example, if you jam or jump, the neck tension node has different levels of sensitivity.

 

[Beetys]

Yes, neck tension is important and has to be coordinated with your style of bullets and seating.

For example, if you jam or jump, the neck tension node has different levels of sensitivity.

Heard. Thanks.

 

[Doghed]

Something that hasn't been mentioned is the use of gauge pins in combination with your expand mandrels. Its pretty simple and quick to check your I.D.

 

[Dave M.]

Hey guys,

I'm very slow.

I'm loading 6.5 creedmoor, and I have a 0.263 expander mandrel.

However, when I run the brass (Lapua) through the mandrel, and measure neck outside diameter, i'm getting 0.2895.

Can someone explain to me what I'm missing?

I was thinking my neck outside diameter was going to be 0.293 (0.263 + (0.015 x 2)) for 0.001 neck tension.

Thank you!!

What type of brass. My Starline 6.5CM box brand new out of the box only measured 13.1-13.5 thou. Assuming you are measuring correctly (using mics and not calipers), .2895” OD would indicate a neck thickness of 12.5 thousandths, when a bullet is pressed in, which isn’t far from where mine were brand new. If you are measuring without a bullet seated, then you are partially seeing spring back and I’m certain your wall thickness isn’t exactly 15 thou. Tell us more about the history of this brass.
dave

 

[Dave M.]

Laurie,
You are really missing out on true accuracy if you’ve never tried anything over .001” neck tension. Break down and buy a few bushings and then let your gun tell you what it likes, instead of you telling your gun it’s getting .001” neck tension whether it likes it or not.
Dave

 

[Bc'z]

Another thought is to skip the mandrel altogether.
I have bushings from .286-.291,
I have 2 really good loads using different powders with the same 123gr scenar and Peterson brass.
With IMR4166 I use a .286, whereas with AA2700 I use a .288.

 

[fkimble@charter.net]

Have you actually measured your mandrel to confirm it;s actual size?

Frank