Initial Neck Turning / .284 / Doughnut Causing wobble

[pat fulghum]

(Sorry for the long post)

My .284 neck turned cases (6.5x284 necked up) do not have a very consistent thickness when I compare them to my 6mm BRAI brass. With 6mm I can hold .00025 thickness variation pretty easy, but unless I do LOTS of work a single .284 cases will differ by as much as .001. Is this too much variation? I think so.

I use a 21st Century Neck Turning Lathe.

So I tried several things to get consistent thickness and I wanted to share my findings. What I found was that the doughnut at the neck shoulder junction isn't perfectly round and that the case would actually wobble like .0005 and that would cause the issue. Let me illustrate, the doughnut has bee highly exaggerated to make my point.

In this picture



The neck of the brass is riding on the mandrel fine and I'm getting a great consistent cut, BUT.

Below, as the doughnut passes over the Mandrel the brass will open up some.. and the brass will start to wobble using the doughnut as a pivot point ever so slightly and change the thickness as it rotates.





Exaggerated below...




If I follow this routine.

1. Anneal
2. Neck Up to 270
3. Neck up to 284
4. Forster Full Length Size / Dwell
5. Expand / Dwell
6. Expand / Dwell
7. Expand / Dwell
8. Forster Full Length Size​
9. Expand / Dwell​
10. Expand / Dwell​
11. Expand / Dwell ​
12. Expand / Dwell​
13. Neck Turn​

I can minimize the doughnut and get much more consistent neck thickness, but man it takes a long time.

There has to be a better way.

Thoughts?

- Pat​

1. ​

 

[Keith Glasscock]

Ream out the donut before neck turning. I have a Wilson cutter that cuts right at .2815 for the purpose.

 

[Keith Glasscock]

Or, you could ream it out while turning:

http://kmshooting.com/carbide-cutting-pilot.html

 

[Cowtownup]

Are you talking about new brass that has been necked up or once fired brass?

 

[Hanbleceya]

(Sorry for the long post)

My .284 neck turned cases (6.5x284 necked up) do not have a very consistent thickness when I compare them to my 6mm BRAI brass. With 6mm I can hold .00025 thickness variation pretty easy, but unless I do LOTS of work a single .284 cases will differ by as much as .001. Is this too much variation? I think so.

I use a 21st Century Neck Turning Lathe.

So I tried several things to get consistent thickness and I wanted to share my findings. What I found was that the doughnut at the neck shoulder junction isn't perfectly round and that the case would actually wobble like .0005 and that would cause the issue. Let me illustrate, the doughnut has bee highly exaggerated to make my point.

In this picture

View attachment 1034058

The neck of the brass is riding on the mandrel fine and I'm getting a great consistent cut, BUT.

Below, as the doughnut passes over the Mandrel the brass will open up some.. and the brass will start to wobble using the doughnut as a pivot point ever so slightly and change the thickness as it rotates.

View attachment 1034060



Exaggerated below...

View attachment 1034061


If I follow this routine.

1. Anneal
2. Neck Up to 270
3. Neck up to 284
4. Forster Full Length Size / Dwell
5. Expand / Dwell
6. Expand / Dwell
7. Expand / Dwell
8. Forster Full Length Size​
9. Expand / Dwell​
10. Expand / Dwell​
11. Expand / Dwell ​
12. Expand / Dwell​
13. Neck Turn​

I can minimize the doughnut and get much more consistent neck thickness, but man it takes a long time.

There has to be a better way.

Thoughts?

- Pat​

Is annealing beforehand necessary? I assume brass you are using is factory annealed. Hardness is optimal.

Slow, steady pressure when sizing allows the brass to ease into conformity. Just my thoughts on this-fewer dwell periods could be used? Seems like some dwell between neck size-ups would be in order.

If you are moving the shoulder at all at each sizing you are pushing brass downward, then sizing up, etc. Several opportunities here for bulge to become distorted in some at least minor way. Hence, bushing dies that allow centering can mitigate distortion.

Using a bushing die to allow centering?

Are you following typical owner manual instructions? All that I have seen say to run ram to shell holder, then turn in one fourth to one quarter turn. That will bump the shoulder. I back it off instead, until it stops just short of the shoulder. Bumping is for later, and then only when measurement indicates the need, or, if you use the bolt felt pressure method, no pressure is felt.

Very light initial pass on turner first, then deepen cut. My sense is that pressure on the cutter as it hits the bottom of the radius of the bulge is possibly causing canting. But then I use a Hornady, that has way too loose of tolerances.

Consider what the other respondents have written about addressing bulge INSIDE of the neck. Very important, but do make good decisions that are not based on opinions that are not backed up by proven methodology.

I have omitted some information here and defer to future posters with perhaps more accurate methods and sounder advice. I just wanted to give you some food for thought and to help you seek your answers from a more informed position. I am relatively new to reloading but I have learned how to ask questions with aforethought so the answers will more readily understood.

Your graphics are amazing. They really communicate clearly. Excellent.

Do hope I have helped in some small way.

Good luck, Pat.

 

[Jay Christopherson]

(Sorry for the long post)

My .284 neck turned cases (6.5x284 necked up) do not have a very consistent thickness when I compare them to my 6mm BRAI brass. With 6mm I can hold .00025 thickness variation pretty easy, but unless I do LOTS of work a single .284 cases will differ by as much as .001. Is this too much variation? I think so.

I use a 21st Century Neck Turning Lathe.

So I tried several things to get consistent thickness and I wanted to share my findings. What I found was that the doughnut at the neck shoulder junction isn't perfectly round and that the case would actually wobble like .0005 and that would cause the issue. Let me illustrate, the doughnut has bee highly exaggerated to make my point.

In this picture

View attachment 1034058

The neck of the brass is riding on the mandrel fine and I'm getting a great consistent cut, BUT.

Below, as the doughnut passes over the Mandrel the brass will open up some.. and the brass will start to wobble using the doughnut as a pivot point ever so slightly and change the thickness as it rotates.

View attachment 1034060



Exaggerated below...

View attachment 1034061


If I follow this routine.

1. Anneal
2. Neck Up to 270
3. Neck up to 284
4. Forster Full Length Size / Dwell
5. Expand / Dwell
6. Expand / Dwell
7. Expand / Dwell
8. Forster Full Length Size​
9. Expand / Dwell​
10. Expand / Dwell​
11. Expand / Dwell ​
12. Expand / Dwell​
13. Neck Turn​

I can minimize the doughnut and get much more consistent neck thickness, but man it takes a long time.

There has to be a better way.

Thoughts?

- Pat​

Whew, that looks like a ton of work. No way I could handle all that. Maybe you should ask yourself "does it matter" (on paper)?

 

[Cowtownup]

I'm curious how you made those graphics.. They are great..

 

[pat fulghum]

Whew, that looks like a ton of work. No way I could handle all that. Maybe you should ask yourself "does it matter" (on paper)?

As you know I have been struggling with 284 consistency, but my 6 is very consistent measuring and on paper. I’m trying everything to get my 284 to be consistent. I have 80 pieces of “super prepped/no doughnut” brass. I will know shortly if it shows on paper. Everyone says consistent neck tension is key and different brass thickness should change the tension. (lee collet has been on order for a bit)


@Cowtownup , Graphics are just a simple PowerPoint then screen shots.

@Hanbleceya, yes this is the initial turning before any firing. Brass will harden just sitting around and my AMP annealer will make it very consistent.

 

[mikecr]

You're creating donut with all that necking up & FL sizing.
What I do here is simply turn the necks new out of the box(never fired or FL sized). Trial & error a few to get them necked up at target thickness. Doing this, remember necking up thins them a bit, and be sure to turn onto shoulder slightly to mitigate donut formation at final size.

 

[pat fulghum]

....
What I do here is simply turn the necks new out of the box(never fired or FL sized).
....

Do you turn before or after the neck up? The process of necking up to 7mm is what causes the initial doughnut that I’m talking about. That initial doughnut is what causes the pivot point on the mandrel

If you use a tube micrometer as shown below i can measure that the neck thickness varies by almost .001 on a single given case. (Yes that is a 6mm in the pic as I didn’t have a 284 pic handy)

Maybe my OCD is kicking in?

 

[LA50SHOOTER]

Ream out the donut before neck turning. I have a Wilson cutter that cuts right at .2815 for the purpose.

I agree with Keith, K&M makes a mandrel as well, that has a cutter integrated into it to help get rid of the doughnut that you may want to consider.

 

[pat fulghum]

View attachment 1034133

I agree with Keith, K&M makes a mandrel as well, that has a cutter integrated into it to help get rid of the doughnut that you may want to consider.

What is the diameter of that K/m reamer with cutter?

 

[memilanuk]

What is the diameter of that K/m reamer with cutter?

Typically its your turner pilot... so for .308 it is, well, .308". You have to size back down afterwards if desired.

 

[mikecr]

Do you turn before or after the neck up? The process of necking up to 7mm is what causes the initial doughnut that I’m talking about.

Before necking up.
You have the best chance of success with standard mandrel fitting & turning of NEW brass.

Take a few new cases that exhibit very high thickness variance. These should be thrown away anyways. Turn one, expand to desired cal, measure neck thickness, adjust & repeat until your turner setting provides what you need. That is, if the first case measures 1thou too thin, cut 1thou less on the next cull, etc.
If your turning is not mitigating donut formation on necking up, adjust the turn onto shoulder until it does.

 

[LA50SHOOTER]

What is the diameter of that K/m reamer with cutter?

They make them in most standard calibers. - Their website lists them

 

[pat fulghum]

They make them in most standard calibers. - Their website lists them

@milanuk and @LA50SHOOTER ,

The reason I asked about diameter is that this 7mm internal neck reamer from Wilson is actually a bit bigger than .284 and if your expander is only .284 (and you get some spring back) it kinda makes a mess of things.

 

[LA50SHOOTER]

@milanuk and @LA50SHOOTER ,

The reason I asked about diameter is that this 7mm internal neck reamer from Wilson is actually a bit bigger than .284 and if your expander is only .284 (and you get some spring back) it kinda makes a mess of things.

View attachment 1034142

View attachment 1034143 View attachment 1034142

I'll be honest with you, And I'm not trying to imply that what your doing is in any way incorrect. - I find that the K&M Mandrel with the inside neck reamer to be a better solution for solving the "dreaded doughnut" in brass than the inside neck reaming tool that Wilson or Forester provides.
What I found was using the Wilson & Forester I was not able to control tolerances as well as I prefer too. If you look at the K&M mandrel you can see the way that it cuts is just with the end of the cutter on the mandrel so its not removing material except at the doughnut area & it is integrated into the turning mandrel. - They are not cheap but they IMO provide one of the best solutions for this problem.
I'm not able at this time to provide you exact measurements on the mandrel, but it is what would be considered as a standard caliber specific neck turning mandrel for the K&M neck turner.

Regards, Ron

 

[Keith Glasscock]

I'm thinking that the K&M turning pilot with a properly sized expander might be the optimal solution. Now if you could expand, resize down, and then just expand the part of the neck above the donut, you might get a better result.

Sounds like an experiment to me. I might have to try it the next time I prep up new brass (probably this year).

 

[ronemus]

Use a sizing mandrel as your last step before turning; that will move the donut to the outside where you can turn it away. You'll probably want to turn in two passes - a rough cut to get everything close and a fine pass to make the neck xall exactly the right thickness.

 

[Hanbleceya]

You're creating donut with all that necking up & FL sizing.
What I do here is simply turn the necks new out of the box(never fired or FL sized). Trial & error a few to get them necked up at target thickness. Doing this, remember necking up thins them a bit, and be sure to turn onto shoulder slightly to mitigate donut formation at final size.

Took a bit of convincing to get me to just edge into the neck. Seemed dangerous at first. Now I understand the mechanics of it. Other readers need to be aware of how deep they cut and that there are different cuttersavailable for different shoulder angles.