The "dreaded donut"

[6.5-300 BEE]

Been messing about with guns 60+ years and never heard of this until a few years ago.

Could someone explain in SIMPLE terms:
1.What it is
2.How to find it
3.Why it's bad
4.How to cure and prevent it

Thanks !

 

[Laelkhunter]

I guess you are referring to the carbon ring?? It forms in the area in front of the chamber (between chamber and bore) of the rifle, and is very hard, sometimes causing an increase in pressure. Can be removed with carbon cleaner, and/or elbow grease, bore brushes wrapped with a cleaning patch and JB paste, etc. Find it with a bore scope. Just take my word for it, it's bad. Cleaning with carbon remover after shooting will help cure and slow it down, but you can't avoid it. Like death and taxes, it can't be avoided if you shoot your rifle.

 

[Elk Hunter 338]

I think he's talking about in the brass inside the neck where the shoulder junction is, and it forms a slight bulge AKA doughnut inside the total circumference. happens a lot when you size bras down.

its not really that bad and its not going to end your shooting carrier ha ha

many people make it out to be something way worse than it is

 

[Beluebow]

Been messing about with guns 60+ years and never heard of this until a few years ago.

Could someone explain in SIMPLE terms:
1.What it is
2.How to find it
3.Why it's bad
4.How to cure and prevent it

Thanks !

A donut is formed where the neck shoulder junction meet.

One easy way to check is to drop a bullet in the neck of a fired case. If it stops you have donut more than likely. And also assuming you have plenty of neck clearance.

It's only bad if you have to seat the bullet in the donut region...Out in front of the donut is no issue.

 

[BountyHunter]

The donut is a ring of brass pushed out at the top of shoulder/bottom of neck junction. It can be caused by brass flow during firing up into the neck shoulder junction causing a donut of brass higher than the corresponding neck. When you resize the case, it pushed it to the inside of the neck and when you insert a bullet, that pushes it back out. The answer is two fold. If you neck turn any, cut barely into the shoulder to allow for the brass flow to start with. Or if it happens afterwards, use an expanding mandrel to push the brass back out and then neck turn again just enough to clean up the donut (ie pushed out brass). It can prevent cases from chambering if it flows too much. It is common on brass necked down IF you do not neck turn.

see the pic below and brass in middle, it is just starting. Brass on right it is clearly formed.

Second pic is how the shoulder should look after turning

 

[6.5-300 BEE]

AH HA thanks.

So this is not the same as the dreaded "carbon ring" I have also read about and have no idea what it is either.

 

[BountyHunter]

No the carbon ring is a ring of hardened powder fouling and carbon at end of case mouth and end of chamber. Already discussed with videos here. Proper cleaning will prevent it from building up, as once it builds up it is a bitch to get out.

Carbon ring?

I realize these aren’t the best pics and that it would be better if I had a 90* Hawkeye attachment, but I don’t have a Hawkeye nor do I know someone who does. Given all of that, does this look like a carbon ring right at the end of the chamber where it transitions into freebore? It is very...

www.longrangehunting.com

 

[Laelkhunter]

This type of donut is news to me, as you can tell by my reply (#2 above). Once again, I have learned something new. Thanks to those "in the know" that have replied.

 

[Bob Wright]

I just corrected 40 brass that developed it, as I seat below that junction with mono bullets. It was significant seating pressure to get past it. Just as in post 5 above, exactly how I fixed mine, with tools I had on hand. I also went to a Redding S full length bushing die after neck turning. Much better.
I had Nosler 280AI brass.

 

[L.Sherm]

It seems to happen more on necked up brass because you open the necks down into the shoulder but it can happen on necking down to. Like stated above turning into the necks helps and having enough freebore in the chamber to get out of the ring solves the problem. I have a turning mandrel on my K@M that has the cutter to cut out the ring on my 30-28 works pretty slick.

 

[25WSM]

Using the cutter mandrel is the best way to keep it gone. If you just use a regular mandrel and run it through the brass donut gets pushed to the out side and will need neck turned again to remove. I leave most of mine go because I seat Above that junction for everything I load. I set my Chambers up to accommodate bullets I'm using.
Shep

 

[BrentM]

I use a Sinclair expander mandrel and it has ended the issue for me. The other options are to inside neck ream, which I've not done, or run bullets on the bearing surface past the junction point each time, or turn the brass right to the shoulder junction. I've turned brass when the bulge appears at the bottom of the neck bushing end point.

 

[6.5-300 BEE]

Now that I think back, I did have a 243 that created donuts. Once rechambered to 243 AI that ended.

 

[ronstone09]

Been messing about with guns 60+ years and never heard of this until a few years ago.

Could someone explain in SIMPLE terms:
1.What it is
2.How to find it
3.Why it's bad
4.How to cure and prevent it

Thanks !

The donut is a small ring that developed inside fired cases ! Usually it won't bother you because you won't seat that deep ! They say when you outside neck turn it clears up !