Gentleman,
Please explain this phenomenon and how to prevent or correct.
Thanks you.

Seems to most commonly occur when part of the shoulder becomes part of the neck. For instance when a case is necked up to a larger caliber (perhaps 7mm-08 from .243) or if a case of formed into a shorter one (e.g. making .308 from .30-06). It doesn't always happen and I am sure there are other circumstances in which it may occur .

I gather the best fix is to run a mandrel or expander into the neck to push the donut to the outside and then turn the neck to remove the excess

I just ream the inside of the neck after sizing.

I get them from making 300 Win into 7 Mashburn Super. The shoulder of the 300 becomes neck and will make a helluva doughnut.

I simply size the necks down and then expand to the donut then turn them out with the K&M inside neck Reamer.

Inside is reaming, outside is turning.

With which tools?

Also can occur with bushing dies that don’t size the entire neck or if you partial neck size with standard dies. Easiest way is to remedy is to either neck ream or neck turn which pushes the donut out where the excess gets turned off. Usually donuts don’t return if you neck turn.

mathman, I just got off the phone ordering a couple of reamers for my Forster case trimmer.

I hope they don't negatively affect neck wall concentricity.

50-50 shot at best which is why I neck turn.

No offense but I suggest you call them back to cancel that order and get one of these:

https://www.forsterproducts.com/product/outside-neck-turner/


Also the appropriate pilot(s).

I ordered both. One method should work. chuckle. I'm just a hobby machinist, but reaming seems to be more logical way of doing it. Though, I question the precision of their trimmer and collet system for reaming. I see a .2- 1.2" inside mic in my future . My old Brown&Sharpe starts at 1/2". I picked up a Forster trimmer at the gunshow Sunday, all the pilots and collets still sealed in their envelopes for $85CND/$63USD.

I'm not aware of a way to prevent donuts. Shoulder material is flowing under pressure and cannot make the turn into the neck.

I ream with the appropriate tooling for either LE Wilson or Forster. The Forster does not support/align the case as well, but you can ream and trim the brass at the same time, so I normally use the Forster setup. I also use a power screwdriver on the Forster trimmer, so the process is really fast.

Another option is to turn necks, and turn very slightly into the should to create space for the brass to flow.

Try both reaming and turning and see which you prefer.

I seem to get donuts within 3 firings in 243win; other chamberings take twice as long.

One thing not yet mentioned is that if the bearing surface of your bullet when seated is above the donut it is not a problem.
If the bearing surface does go into the donut, neck turning is the way to go

Reaming will perhaps eliminate a donut, but only makes a bigger hole and does nothing to improve neck wall uniformity. If necks aren't uniform, you will have runout in loaded ammunition. Maybe not a big deal, but if going to all of the trouble would suggest sizing full length, expanding the necks with an appropriate mandrel, and then outside neck turning. As mentioned previously, best to kiss the shoulder with the cutter too, for the base of the neck will become shoulder when the case is fire formed and therefore donuts not an issue.

I'm somewhat perplexed by the donut problem, for only have known this problem with tight neck chambers, usually where case necks weren't cut fully down to the shoulder. I have cases that were fired 40+ times and never an issue. But for these I don't drag an expander ball through the necks either.

It occurs in other circumstances. I had brand new WW brass in 7mm-08 with donuts as they came.

Another good reason not to buy new Winchester brass. I’ve seen the same thing.

If I've gotten them I was both unaware of it and it wasn't bad enough that it ever caused an issue with either accuracy or pressure. I get long case life generally through a lot of loadings in a lot of different cartridges and it never shows up. I also use an expander ball so it's not that, at least not with me.

The ONLY time I seen it ever so slightly was after numerous loadings like 5 or 6 in a 35 Whelen, and each time it was loaded with a short bullet intended for 35 Remington. The Whelen with its long neck makes the base of those short bullets out the neck pretty far even when seated as deep as possible. I eventually could feel a slight ring just behind where that base was sitting. As already stated as long as I don't seat below that slight ridge with a different bullet, I don't see it will be a problem.

Those Whelen cases were expanded up from 30-06. No clue if that has anything to do with it or it is solely because of loading short bullets out the neck.

It's a likely cause. When necking up you get what was shoulder material becoming the lower portion of the neck.

got a really bad case of the donuts when I used Hornady match brass in 308 and try necking it up to 358.

Does necking up in steps make a difference? Or none? I use the Hornady expanders when necking up since they are tapered and make life easier. I made sure I had plenty of lube on the inside of the necks and necked up to .358 in 1 step. It went well, didn't lose a case.

I necked up a 6mm case to fire form in a 257 Ackley because I have plenty of 6mm cases so I figured that would be a good source for me. I went bigger than .257 initially to create a false shoulder. That worked out just peachy as far as fireforming but I haven't reloaded that case anymore.

If donuts are gonna be a problem from doing that I might have to get a neck turner and learn how to use it. Crap. My reloading room is starting to become disorganized so as it is.

I also prefer to turn the excess off the outside. It makes the case necks a uniform thickness.

If the case is thicker on one side than the other, a reamer will follow the hole and the neck will still be thicker on one side.

I can also keep the case and neck straight when turning but I don't have a lathe to keep a reamer straight.

As always, your mileage may vary.

I get donuts with Lapua brass in my NULA 22-250, it has a tight chamber. American brass works great and I usually just use Winchester.

That sucks. You should try some Sig brass. See how it does. Although, I thought this was a thread about sticks quadruple chins AKA "neck donuts"..

Necking up 243 brass to 260 educated me on donuts. Outside neck turning just uniforms the outside of the neck and doesn't effect the donut which is formed on the inside. When you seat the bullet the material on the inside causes the neck to expand possibly creating clearance issues, maybe squeezing the bullet if the rifle has a reasonably tight neck. This can cause high pressures but no matter what it makes for uneven neck tension. I did get away with using 243 brass some brands were OK. I ended up using 7-08 (best) and 308 brass which some brands needed the necks turned due to general thickness. I found some Nosler brass at a gunshow and bought 200 cases, though many say it is crappy brass this lot turned out to be the best I came up with for my 260.

How do you determine if you have a donut? Visual? Measuring or feeling with some kind of gauge? This is all new to me, so please excuse my ignorance.

Not so.

Before turning the neck, I push the neck over an expansion mandrel. This pushes the donut to the outside, and it sizes the hole in the neck to be a close slip fit on the mandrel in the turning tool.

Fired case, slip a bullet in down to the neck/shoulder junction. If the bullet stops or meets resistance before that you gots a donut.

I should think pin gauges after FL sizing would be the best way.

Lapua 22-250 brass is kind of a unique problem, it exceeds SAAMI spec's !!!!!!!

About 20 years ago I had my own 22-250AI reamer made, it was based off of Norma and Federal brass. Winchester and Remington were the smallest to SAAMI spec so I never had an issue with any of it until Lapua came out with 22-250 brass about 10 years ago.
I had an issue the first time I used it and found by measuring that it was bigger in every dimension than every other brand on the market. It works fine in most sloppy factory chambers but not in a tight chamber.

Lapua has suspended production of 22-250 brass, they might have realized they had an issue

I might give it a try, the brass that is.


That’s exactly my experience.

I tried a small hole gauge ,it's very much a feel thing. As such, a clean inside of the neck would be necessary . Good idea, using a pin gauge. I'll see if I have the correct size pin.

There will still be some spring back. To me the best way to go is use brass from a cartridge that starts out with a larger diameter and neck down. Or seat the bullet where the base (full diameter) is above the thicker metal. At least this is what I did to suit what is probably the most accurate barrel I have owned.

Mathman is correct. The mandrel pushes it to the outside but some folks forget to turn slightly into the shoulder where the donut material resides. First firing brass flow will fill in the slight gap and 99% of the time donuts don’t reappear.

So you are saying that you feel the inside of the neck is parallel after being outside turned on a mandrel? If the case had a pronounced "donut" and the mandrel pushes it out is the mandrel supporting the rest of the neck evenly? In my humble estimation best results happen with outside neck turning when the neck ID is straight and without a lump on the inside. But good luck with all that.

The neck is sized small enough that the expansion mandrel is in interference fit contact with the neck even before it gets down to the donut. It's not just pushing out the donut.

As to good luck, the cases I process by this method subsequently size dead straight. Something must be going right.

Don’t think he will read it but good article on neck turning. Even covers the dreaded donut.

https://coyotestuff.com/case-neck-turning-step-by-step/

So when the donut hits the mandrel and pushed off of it doesn't this move metal in front of it off the mandrel a bit? This would seem like it would cause the case neck ID to vary at that point compared to the rest of the case neck. When I turned the necks for my match ammo I liked to get the outside neck clearance pretty close to .001 or .0015. Now suppose I am turning necks as you suggest but adding that variable? Now if you are just building brass for a hunting rifle sure, clearance is all that matters.

I have not observed that problem occurring.

When you say .001" clearance are you talking loaded neck to chamber? When I was studying up on neck turning I found a lot of serious BR guys who would say that's too tight.

Excellent link. That said the donuts I am considering are those caused by necking up say 243 cases to make 260 Remington cases. Not formed by not turning the necks far enough back. The problem being the thicker material that was shoulder and is now part of the neck. This can reduce inside diameter as much as .004. I think it is better to avoid that issue by necking down from 7-08 or 308 and then outside turning the necks to the diameter that suits the rifles chamber.

I agree it's better to avoid the donut in the first place.

Well it worked but in the end I went with .0015 after a bit of experimentation. I even did the tight neck thing where it wasn't necessary to size the cases just prime and seat a bullet. All just to play around and find out.

What kind of match rifle was this?

A custom on a Remington 700. Had many barrels on it then sold it, bought it back and am presently thinking about putting a 30BR barrel on it for the score matches at a local club. My favorite of all time barrel was a 6x47 Lapua. It is now a 22BR and I am not planning on setting up for that round.

I have been following this discussion.

I use the RCBS Trim Pro 2 manual case trimmer. I have the neck turning tool for it which can be adjusted to turn 22 to 50 caliber brass. The pilot for each caliber includes a cutter on the end.

Is this pilot/cutter sufficient to remove internal donuts?

I usually set the turning tool to just touch the neck on the outside, to take off any high spots.

I size 7x57 and 6.5x57 to 6mm Rem. 243 to 260 Rem, 308 to 260 or to 7mm-08, 284 Win to 6x284, and finally 243 to 22-243AI.

just an interesting note: In the case of the 6.5 x57 to 6mm earlier this year, I found my Redding neck sizer would not sufficiently size brass to fit the chamber of my rifle. I had to purchase an additional FL sizer. The FL sizer was not easily available a few years ago when originally shopping for 6mm dies.

Yep it will take care of the donut.

Using a Lee collet die and turning the excess off as it grows from the shoulder - neck area.

The collet puts the donut on the outside, where it is easily turned off.

Thank you for the confirmation.

It will work but probably the worst case scenario Ican think of

Since you use one expand the answer.

Please expound.