What's causing donut ring in case

2

27-T

Member
Gentlemen - Why am I getting a donut ring, inside the case neck, on some cases and not on others? I loading 6mm PPC with both Lapua and Norma brass. My chamber neck is .263 and it's a Shilen barrel.

The cases are trimmed to 1.490" length, sized in a Redding small base die with their .259" sizing bushing. All necks are turned to .0085 neck wall thickness. The shoulder is being bumped a very minor amount, just enough to be even with a Wilson case guage.

Some cases have the ring and some don't.

If you have any ideas or suggestions, I would love to hear them.

Thanks,

Jim
 
The simple answer is:

Your brass is thicker the farther down from the mouth you go. Neck turning only gets rid of some of the fatter stuff from the outside of the neck, and the shoulder material eventually ends up working its way forward, thus giving you a donut. We also don't help matters with bushing dies that only size 3/4 of the neck itself. The material there in the middle is getting squeeze-stopped on one end, and pushed up on the other.
 
Are you seeing the differences on paper between those that have the donut and those that don't? Unless you're seating below the neck / shoulder junction (which I assume you're not with the PPC), it may be best to leave well enough alone. The other option is to ream them.

-Lee
www.singleactions.com
 
I haven't noticed any difference in the groups. Maybe your right - "leave well enough alone".

As for the bushing sizing - about 3/4th of the way down the neck is the best I can get. Can't get it to size any lower on the neck without destroying the shoulder. This is all the deeper the bullet is seated anyway (approximate).

Thanks guys,

Jim
 
Another thing...I do not believe that a Wilson case gauge is the best tool for keeping track of head to shoulder dimensions, when trying to be precise. I have a "headspace tool" that was made by Stoney Point (now sold by Hornady) that I use for these chores. Just about everyone that I know that is interested it precise reloading uses something that gives them readings in thousandths. On the doughnuts, since your seated bullets' bearing surfaces probably do not come anywhere near them, I would not worry about them at all. You are just pushing up thicker shoulder material into the bottom of your necks when you FL size. How often are you having to trim, and how much? The mismatch between die and chamber and the setting of the die with regard to bump both play heavily in how fast your cases grow, and whether and when you get doughnuts.
 
Don't have to trim very often. When I do, it's usually .002 to .003 to keep constant.

Thanks for your input.

Jim
 
Insufficient shoulder setback

On new 220 Russian brass, set the shoulder back 0.015" with an appropriate FL sizing die (I use a 220 Russian FL sizer), then expand with the neck turning expander mandrel.

This will make the neck-shoulder junction (which moves forward after fire forming) into a parallel straight section that will be turned away. This will eliminate the doughnut.

I use a shell holder shortened by 0.015" to enable sufficient shoulder setback. If you modify a shell holder, remember to mark it clearly so it won't be used incorrectly with a regular sizing operation. Although, the latter is unlikely since no other common cartridge uses the 220 R case head size.

Greg Walley
Kelbly's inc.
 
Greg Walley said:
On new 220 Russian brass, set the shoulder back 0.015" with an appropriate FL sizing die (I use a 220 Russian FL sizer), then expand with the neck turning expander mandrel.

This will make the neck-shoulder junction (which moves forward after fire forming) into a parallel straight section that will be turned away. .
Click to expand...




Greg,

Are you turning twice to accomplish this? Once before fireforming and once after? Or do you have a dedicated fireforming barrel with a .273" neck or something along that size?
 
goodgrouper said:
Greg,

Are you turning twice to accomplish this? Once before fireforming and once after? Or do you have a dedicated fireforming barrel with a .273" neck or something along that size?
Click to expand...


No fire forming is required before neck turning with my method mentioned above. Size with setback, expand, turn (I do it in one cut) then fire form.

Greg Walley
Kelbly's Inc.
 
Another vote...

The "doughnuts", as they are called, were once a great point of contention. It is now known that they don't make a difference as long as the bullet seats without touching.
 
I have been fire forming before neck turning for a number of years. When you size it for the neck turner, the bulge is then on the outside, which is then turned away.

But even with that, a slight donut will still form after repeated sizing. Metal is moving.

But as Wilbur noted, it has been concluded that as long as the bullet doesn't get down there, it is of no consequence.
 
Jackie,
Although I have absolutely no experience turning necks on a lathe, if I understand your procedure correctly, you have the mandrel turning with the case and a slight interference fit of the neck on the mandrel, which would force any excess thickness at the neck shoulder junction to the outside, where it would be removed as the neck is turned.

When I have returned cases that have developed a slight doughnut with a hand held tool, even though the expander pushed it to the outside, it would spring back to some degree, tightening the fit of the neck at that point. To get around this, I have done things like leaving the case on the expander for several seconds, and double stroked the press when expanding, but none of this does a perfect job, so it seems that there is at least one real advantage that lathes have for turning (and returning) necks.
Boyd
 
Greg Walley said:
No fire forming is required before neck turning with my method mentioned above. Size with setback, expand, turn (I do it in one cut) then fire form.

Greg Walley
Kelbly's Inc.
Click to expand...

Thanks for clearing that up Greg. I have tried that method and found I still got donuts eventually, though not as fast as some of the other methods.
 
jackie schmidt said:
I have been fire forming before neck turning for a number of years. When you size it for the neck turner, the bulge is then on the outside, which is then turned away.

.
Click to expand...

I have been doing this method for several years. I think it's still my favorite. But as you said, the donut still eventually shows up.
Really, truly, the only way I've found to get rid of the donut is inside neck reaming and doing it several times. But even then, it's near impossible to get the absolute perfect sized reamer so as not to avoid a shelf inside. So there's still an "anomaly" in there and in the end, after many hours spent trying to fix the problem, I started looking at the results of the problem instead. It was by this approach that I found that the dreaded donut is way overblown in importance, and not a problem at all.

Even in cartridges other than the 6ppc (yes, been neck turning for the big guns for far longer than 6ppc's), the donut can be managed. I've found that with any hunting bullet or VLD, it's near impossible not to seat your bullet into the donut. Remarkably, as long as the load is reduced to compensate, the donut won't affect a thing.
 
Boyd Allen said:
which would force any excess thickness at the neck shoulder junction to the outside, where it would be removed as the neck is turned.
Click to expand...

I just haven't found that to be the case (no pun intended). The bulge there doesn't get completely "pushed" to the outside. It can't unless the medium is non-solid. You can't force that solid material completely to the other side of the center line without some of it coming back.

Take an inside ball mic and measure the thickness of the neck (after turning) near the neck/shoulder junction. (Make sure your flat on the post side is not interfering on the shoulder. You may have to alter the size of the flat if it is). It will always be a bit thicker in that section no matter how many times you ran an expander through the neck. The excess material is on the inside and it didn't get turned away. It can only be reamed away.

The good thing is that none of it matters as has already been said. It's all just fly poop in the pepper. Turn your brass, shoot it, replace it when needed. Don't waste your time messing with this stuff unless you really want to understand the imperfections and implications of what we do.
 
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Aged brass doughnuts (that doesn't sound appetizing!)

jackie schmidt said:
...But even with that, a slight donut will still form after repeated sizing. Metal is moving. [snip]
Click to expand...

I never thought of checking my brass after repeated firings for a doughnut formation from brass flow and sizing. I cut my necks thin enough to allow for a bullet to pass through the fired case neck with no resistance. But with my freebore dimensions (even on my big guns with tight necks) the bullet base doesn't seat past the neck-shoulder junction. I'll have to get some of my old brass and check for the restriction with a gage pin, or measure the profile ID with a test indicator.
 
A bit of science...the way I see it

If there were no bullet, the donut would make a difference (of some sort) as it would be the smallest restriction. Given that the bullet completely plugs the barrel it overrides the restriction of any donut. If the bullet seats in the donut, it affects accuracy by creating tremendously variable pressure before the bullet leaves the case neck. If your chamber neck is larger than the loaded round, it very well could not matter.

Donuts and case neck length are somewhat similar...and I know for sure that you won't win a benchrest match when your case necks are too long. Never allow a restriction on the bullet that's not built in.
 
Why use small base die

John - I use the small base die because it was recommended to me by the tech guys at Sinclair.

Jim
 
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