I've necked up and down in the past and generally not worried about it.

But I'm starting to wonder if I shouldnt stop that practice due to the donut factor.

Anyone ever found the dreaded donut in your neck ?

i don't think that is a problem unless the brass has been neck turned,to create the ridge which becomes the donut.

Ed

Its suprising on the lack of information on donuts. But IIRC your correct turning necks / reaming and then shooting / full length resize does often put you in bad shape.

For the most part I think typical factory rifles are ok (not a tight neck) with a slightly thicker neck brass. From what I've read the 3-08 to 260 results in a 16% increase in neck brass thickness.

Just wish I could find a few of the old donut in the neck articles.

Spot

Generally it happens either when you neck up and fold some of the shoulder into the neck, or when you neck down a longer cartridge body so that the body becomes part of the neck when you reform. I get it out of Rigby or RUM brass when making something like a Jamison case (similiar to a WSM). As the body stretches, the thicker shoulder begins to fold into the neck and you get the donut.

If you don't seat the bullet all the way into the neck you have no concerns. However, if the bullet is seated deeper than the end of the neck, it can become a problem, especially if the neck is tighter than production chambers. For other cartridges where brass is commonly available, I've never found it to be a problem, even in custom chambers. It's fairly easy to check and in fact, if serious, you can feel the doughnut when you seat a flat based bullet. It's more difficult to feel with a boattail. The easiest check is to mike the neck after you seat the bullet both at the mouth and at the base of the neck where a doughnut might be located. If the difference is more that a couple of thou's, better be careful!

If you measure fired brass out of that chamber at the base of the base of the neck, you can measure the reload at the same location. If the reload measurement is larger than the fired brass measurement, DON'T fire that cartridge! If less, no problem.

I'm loading for a 30BR, necking up from 6mmBR.
Yep there is a definite doughnut, as the top of the shoulder is now the bottom of the neck.
I'm turning for a tight neck chamber anyway so it's easily turned off while I"m there.

30-06 to 35whelan or 338-06, never had a doughnut problem.

It's not a problem as long as you have a good cup of coffee to dunk 'em in.

I recently bought a rifle chambered for a wildcat AI (6.5/250 Sav AI) and discovered first hand what a donut is. And I didn't have any coffee on hand either.

I had full length resized previously fired (and fire-formed) brass and tested if they would chamber. No problems. The brass was fire-formed from .22-250 Lapua brass

I used a modified case with my Stoney Point OAL tool to find the rifle lands and seated some loads about 0.010" short.

I didn't test again for chambering until I was out at the range where I discovered that the bolt wouldn't close on loaded rounds.

I didn't know about donuts and it took me a good part of this morning to discover the donut at the juncture of the neck and shoulder.

Now it's decision time to either break down my loads and turn necks, or just re-chamber to 260 Rem and not have to fire-form brass in the future.

I have run into the doughnut when forming 256 Newton cases from 270 winchester brass. The Newton case is shorter and some of the thicker brass from the shoulder ends up at the base of the neck. Inside neck reaming seems to take care of it.

The donut can also be fixed by careful outside turning in that area of the neck, but it's probably easier to inside ream.

In general, however, it's why I prefer necking down!

I would give 6.5 Creemoor brass a try before re-chambering. Depends on your chamber but I bet you would be moving a minimum amount of brass as the chambers are so similar.

Likewise I would just bite the bullet and break down what you have, neck ream and reload. Even if you re-chamber you or at least I would pull the bullets and salvage the powder from the AI loads.

I recently formed 300 Savage brass from Fed. 7.62x51 M1a cases. I got donuts in most cases so I ordered a RCBS turning head and 30 cal. reaming pilot for my RCBS manual trimmer. It works great removing the donut.