Home Forums Hunting & Shooting Ask The Gunwriters "dreaded doughnut" - MD

John, I read a while back that you use a neck turner to eliminate the "doughnut"
It seems to me a reamer would be necessary.
Can you school me on the process you use?

I just size the case with a standard expander-ball die. The expander-ball "pushes" the doughnut to the outside of the neck, where it can be lathed off.

What exactly is this "dreaded doughnut"?

It's a thickening of the base of the neck in bottle-necked cartridges, which can result in poor accuracy, or even excessively high pressure, because of the "doughnut" being pressed around the bullet when the cartridge is chambered.

It normally occurs for two reasons:

The process of firing and resizing the cartridge. This tends to move brass forward in the case, and the top of the shoulder (which is thicker than the neck) starts to "migrate" into the bottom of the neck.

Necking cartridges up in caliber, say making .260 Remington cases from .243 Winchesters. Again, the top of the shoulder becomes the base of the neck.

But I have also occasionally encountered new factory brass that had slight doughnuts.

It has been a while but I got some WW in 7mm08 that had bad doughnuts.

Mule Deer, thanks for the explanation.

Why couldn't an inside neck reamer be used to remove it? Does that cause a problem?

K&M makes a handy turning device that cuts in and out simultaneously

An inside reamer can easily remove the doughnut. But that doesn't mean it will leave the neck the same thickness all the way around, partly because with a lot of "standard" mass-produced brass the necks tend not to have the same thickness. This can definitely cause accuracy problems.

Outside-turning not only remove the doughnut but insures even neck thickness.

Ah so. Thanks.

“Doughnuts” have little to no effect on accuracy if you have a chamber that allows the pressure ring on the bullet to be seat above the neck should junction. ( where the “doughnuts” live )If you do have chamber that will allow this, it’s hit or miss that the loaded round will still fit in the magazine. ( assuming you handload )

It’s only a couple or so of the latest cartridge designs that take “doughnuts” into consideration. 300prc comes to mind.

Wouldn't the "donut" issue be mostly confined to match chambers with tight necks?

No. It's a pain in the ass with factory chambers too. It screws up bullet seating.

That sucks, I have necked up 40 or so cases of 243 to 260 and have yet to see anything resembling a problem.

It doesn't always occur.

My experience indicates more problems with cases necked up, rather than down. For instance, necking 22-250 cases up to 250-300 AI. A "doughnut' will develope at the neck shoulder junction. I found this on my 2nd firing of the cases..sized cases chambered fine, but when I seated a bullet, the doughnut was pushed out, making for hard chambering. My normal sequence when loading is to try both empty sized brass in the guns chamber, then the first charged and seated case. So I only had one loaded. I ended up outside neck reaming. Getting a little smarter, I found I could discover the doughnut by fitting a bullet into the fired case. The bullet would stop at it in the neck. Those fired cases I inside neck reamed.
I now use plentiful 6.5 Creed cases, neck down..no problems.

It's one of the reasons for David Tubb's 6XC as well--which is the .22-250 necked up and with the shoulder also pushed back. It will fit in standard shot-action magazine about 2.85 inches long, and even 115-grain high-BC bullets won't seat down into the shoulder/neck junction.

As mathman noted, it doesn't always occur, but can after a number of firing/sizing cycles. Which is why I eventually started necking .270 cases down for my 6.5-06, rather than necking .25-06 cases up.

Thanks, John.

Well I am going to watch that brass. I have annealed the first 20 pieces I got hold of, actual antique Remington 140 gr. Factory ammo. Each piece has been fired at least ten times.Retired. But the 40 or so pieces of Winchester 243 brass necked up is expected to last ten firings also so I will watch for the creeping doughnut. I hated doing it but I necked down a box of 7-08 Winchester brass to 260 and also some PPU 308 brass and another 20 rounds of Federal 308 brass. All have been loaded and fired at least once. Though presently I have slowed my primer popping down a lot.