How to Identify a Neck Donut?

[Roninco]

How do you identify the dreaded neck donut? Can it be seen inside the neck with a bore scope? How many reloading's does it take to form if using a bushing die? Would it not be forced to the exterior if expanding with a mandrel? I just started using a Redding bushing die so I've never had to deal with this before.

 

[L.Sherm]

You can use the end of a paper clip or a bullet slid down the neck of a fired case if it stops you know you have the donut.
You can also feel it with a mandrel when you try to size your cases.

 

[Mikecr]

How many reloading's does it take to form if using a bushing die?

Body sizing rolls brass up the case. Neck bushings contribute nothing to donut formation.

Would it not be forced to the exterior if expanding with a mandrel?

Yes, and also when seating bullet bearing into donut area (but bad plan there).

By process of manufacture, cases are thickest near webs, tapering to thinnest by case mouths. So it is normal for necks to be thicker near neck-shoulder junction than at mouths. In other words, a donut is built in initially.
From there, it is our sizing that contributes to problem donut thickness.
Upsizing necks causes thicker shoulder brass to become neck area (donut formation).
Heavy sizing of case bodies rolls brass thick toward thin (up the case).

Donuts being a problem or not depends. If seating bullet bearing into it, or FL sizing necks, it's likely a problem.

 

[dok7mm]

I use pin gauges to check if shoulder brass is moving into neck. @Mikecr is spot on about dies oversizing your case, that brass goes to neck.

My solution has been to use mandrels and turning the necks + a bit into shoulder. This will delay donuts for awhile, but you have to check for reoccurrence. Another option is to find a load where the bearing surface seats above the neck/ shoulder junction.

 

[L.Sherm]

. Another option is to find a load where the bearing surface seats above the neck/ shoulder junction.

That's the best option if you got the freebore and mag box length.

 

[Roninco]

Thanks for the info. This is a 180 grain ELD-M in a 7mm SAUM so the base is well below the neck-shoulder juncture. This could result in bullet impingement if a donut was forming after several reloads. I am trying to determine how to identify if the dreaded donut is forming. Bullet seating pressure seems normal from previous reloads. But I had to pull some of the bullets and it required far too much effort to extract to believe this was normal. Looking into the necks of the pulled cases I sometimes see a bright ring at the neck-shoulder area. If this is copper residue from the bullet could it be caused by a donut?

 

[Tiny Tim]

Its possible, or it could just be scraping the guilding material off on the neck/shoulder junction. L.Sherm gave a good way to check for it. Some sizing methods and some cartridges are more prone to the dreaded doughnut formation than others. Are you noticing changes in pressure, accuracy, or speed that cause you to question if this is occurring?

 

[Roninco]

Its possible, or it could just be scraping the guilding material off on the neck/shoulder junction. L.Sherm gave a good way to check for it. Some sizing methods and some cartridges are more prone to the dreaded doughnut formation than others. Are you noticing changes in pressure, accuracy, or speed that cause you to question if this is occurring?

On the fourth firing (third time reloaded) the bolt lift becomes stiff, velocity is about the same. On firings one through three the bolt lift is smooth and velocities constant.

 

[L.Sherm]

Are you bumping your shoulders back .002-.003. Could be your brass is becoming tight at the shoulder or .200 line.
Brass has a memory so if your not could be your extraction problem.
Only way to know is measure.

 

[Roninco]

On the fourth firing (third time reloaded) the bolt lift is stiff, velocity is about the same. On the first through third firing the bolt lift is smooth and velocities steady. The shoulder is set back .002-.003" and I have begun annealing after each firing. I trim after fire forming and need to again after the third or fourth firing so case length doesn't seem to be the issue.

 

[Mikecr]

When you have to trim brass here & there, you have a process of donut formation in play.
That brass you're trimming away had rolled upward from lower parts of the case.
It means that with every reload cycle you're changing the entire case (a little bit,, or a lot).

There is NEVER good in excess sizing. Only bad.
2-3thou shoulder setback is excessive downsizing.
That extraction soon gets difficult means high chamber clearances near webs,, that's excessive upsizing.

Yeah, you'll need to include donut management in your sizing plan.
If you have to seat bullet bearing into neck-shoulder junction, and already have plenty of neck clearance (so don't turn necks further), and have to FL size(I don't know what your cartridge is), then consider donut reaming now & then. Just a hair, with fired/unsized necks. It's a last resort IMO, but you might be there.

 

[L.Sherm]

.002-.003 is not excessive downsizing.
To each his own.

 

[Mikecr]

Well, 1thou works good.
2-3thou is just that much beyond.
If you're sizing case bodies or shoulders 2-3thou, it's more than you have to.

More than you have to means changing your brass more than you have to.
It can mean loosening primer pockets, frequent trimming (changing capacity), frequent need for annealing, changing hardness/clearances/pressures/MVs, higher runout/thrown shots, donut issues, extraction issues, headspace issues.
Otherwise, I can think of NOTHING good in it.

Some folks have to FL size, due to early choices. Some believe FL sizing is good.
Some take it further,, if FL sizing is good, then more of it is better.. That's where it crosses over to wrong thinking.
Truly, no sizing/causing change, large or small, is 'good'. It's never free.
So your sizing plan, whatever it is, should manage this as minimal. Do that, and you'll mitigate every issue that I listed here. Reloading just gets that much simpler.

 

[L.Sherm]

Do whatever works for you theres alot of people who have moved away from Neck sizing BR and Hunters.
This has been pounded in the ground.