The ultimate solution to neck tension

[Joe R]

I know that everyone likes to control neck tension with bushings but to me that doesn't seem like a very good way. From my way of thinking bushings transfer any variance in neck thickness to the inside of the neck where they have a direct impact on neck tension. That is not a good thing, because no matter how careful you are turning necks there will be variances, and those variances will impact neck tension.

I believe that the outside of the neck has minimal importance. The only important thing is how thick the necks are because that has an influence on spring-back. IMO the part of the neck everyone should be focusing on is the inside of the neck, or more appropriately inside diameter. The inside diameter is what influences neck tension, if one can transfer neck wall variances to the outside of the case it is that much better.

So the question is how do we control neck tension from the inside of the neck? What if instead of honing die necks (an irreversible and often problematic process because dies are hardened, not to mention that you have to be twice as accurate with a die then with a mandrel, an impossible task) we were to use a mandrel to expand the necks to provide the desired neck tension? What would a mandrel do?

Well, ... a mandrel would control the inside diameter of a case neck much more precisely than any bushing ever can. It could also transfer neck thickness variances to the outside of the neck where it doesn't interfere with neck tension and bullet release. That's good isn't it?

I have been using mandrels for thousands of cases. The problem is that just when I have a mandrel that gives ideal neck tension (down to .0001 precision) it starts to wear, and after a 1,000 cases it is done. Making another mandrel to .0001 precision is very difficult/not possible for most machine shops and grinding shops. So I set out to look for a solution.

Pin gages are small tubes 2" long and can be bought for a few dollars and they are available in dimensions as exact as .0001 (+/- .00002). They generally have a 60 to 62 Rockwell hardness, like tool steel. They are ideal for this purpose, all you have to do is bevel the tip.

Well, ... to make a long story short Kenny Porter (Porter Precision Products in Lake Jackson, Texas) made this die for me last week. The collet he used is made for lathes so it holds mandrels perfectly straight. This mandrel die makes all other mandrel die I have seen or bought look primitive.

Regards

Joe

 

[jlow]

Sounds like a nice idea! The only thing I was a bit surprised to hear is the degree of wear you are seeing, what type of lube are you using?

 

[skiutah02]

Looks like a better mousetrap, nice. Drew

 

[Joe R]

Imperial sizing wax, but I also think that my 308 small base die was constricting the necks too much.

Compliments from the two of you are really flattering, since I have been learning lots from your postings over the years.

Joe

 

[JRS]

Now you need to find perfect bullets to go along with that

 

[savagedasher]

I would line to have perfect internal volume
Larry

 

[1shot]

Just so I'm understanding this, a fired case is going to be larger the bore diameter by some amount, correct? So you would need to run the brass through a resizer to lower the neck inside diameter by some small amount, then use the mandrel die to set your neck tension. Is this correct?
Thanks,

Lloyd

 

[Joe R]

Just so I'm understanding this, a fired case is going to be larger the bore diameter by some amount, correct? So you would need to run the brass through a resizer to lower the neck inside diameter by some small amount, then use the mandrel die to set your neck tension. Is this correct?
Thanks,

Lloyd

Exactly

 

[jlow]

Imperial sizing wax, but I also think that my 308 small base die was constricting the necks too much.

Compliments from the two of you are really flattering, since I have been learning lots from your postings over the years.

Joe

Thanks! Yes perhaps that is one cause of the wear as Imperial should work well.

 

[savagedasher]

When that is done where does the donut go .
Ever time I shoot a case I get some donut starting . Larry

 

[Joe R]

I would line to have perfect internal volume
Larry

And I would like to reverse aging, but that isn't going to happen is it?

 

[Jdne5b]

Did he make the top and die body? Or just the die body? Where can one source the collet and top?

 

[jlow]

Thanks! Yes perhaps that is one cause of the wear as Imperial should work well.

The thing to keep in mind is the over constricting of the neck by a small base die will work harden your necks more, and work hardening over time will change neck tension regardless of the use of the same size mandrel.

The best route forward may in fact be doing a specific anneal to prevent the progression of work hardening and to keep the work hardening to a constant degree. That of course is easier said than done.

Also, the reality of all of these suggested changes is to your current SOP in any of these ways will likely result in a different end result neck tension so I would not make any change without some thought.

 

[22BRGUY]

One question Joe...How much is the die?
Great concept IMHO

 

[dkhunt14]

Looks like it should work. Wonder where the idea of Guage pins came from. LOL. MATT

 

[Joe R]

The thing to keep in mind is the over constricting of the neck by a small base die will work harden your necks more, and work hardening over time will change neck tension regardless of the use of the same size mandrel.

The best route forward may in fact be doing a specific anneal to prevent the progression of work hardening and to keep the work hardening to a constant degree. That of course is easier said than done.

Also, the reality of all of these suggested changes is to your current SOP in any of these ways will likely result in a different end result neck tension so I would not make any change without some thought.

Jlow,
As I understand it, annealing is like a "restart" button on a computer, it takes you back to the beginning. As Donovan Moran once taught me, if you anneal once, you should anneal every time, and I do. My friend Ben Steinsholt took this one step further and he anneals before using the mandrel, and before resizing. I think that was very clever of him don't you?

Joe

Did he make the top and die body? Or just the die body? Where can one source the collet and top?

If you want more specifics you'll have to talk to Kenny <kennethp@portersprecisionproducts.com> . My suggestion to him was to apply for a patent and I believe he will.

Joe

 

[Auto-X Fil]

I love the Lee Collet die idea, but quality is not that good. They always need some tweaking to work well. This looks much nicer!

 

[Joe R]

Looks like it should work. Wonder where the idea of Guage pins came from. LOL. MATT

I'm willing to bet I'm not the first one to think of it, but it occurred to me because I bought a .308 pin to make sure my cheap calipers were working properly. In the process I learned about pin gages. But all the credit belongs to Kenny for thinking of using the precision collets, that's the game changer idea IMO. When you see those collets up close they are a thing of beauty.

Joe

 

[nmkid]

The old thinking cap has pretty much had it...How do you determine the size mandrel you would need?

 

[rardoin]

A quick and easy solution is to take the beveled pin gauge and clamp it tightly in a collet puller (I have a Hornady) in the press....and presto (pun intended) you have a neck expansion die. The case float in the holder will allow for self centering. KISS principle.

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