Home Forums Reloading Big Game Rifles Neck donuts

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.