Talk to me about the dreaded case neck "Donut"

[ReaperDriver]

So what is the donut, how does it get there and what effect does it have on loading and load performance?? I suspect I have donuts in my Lapua case neck as I'm getting signs of pressure in a gas gun when there should be none. Due to some pressure signs of swipe and ejector marks in what I would have thought to be fairly average moderate loads, I just re-ran a load test basically a full grain less and I'm still getting swipe.

The reason I suspect the "donut" is because when you slide a bullet into a fired neck, it feels like it hits a stop right around the shoulder/neck junction and my shooting partner said "It feels like a donut".

The lighter load where I'm still getting pressure and swipe is in a .260 gasser, 22" JP barrel w/ headspaced High pressure bolt, Lapua 3x fired brass, 41.9 gr of H4350 with 130 Berger Hybrids (2792 fps). The other load is 123 scenars @ 42.4 H4350 (2870 fps) that I'm getting even more pressure and swipe with.

Any thoughts would be appreciated. TIA

 

[2aBaC̶a̶]

What kind of dies and sizing process? Are you using a bushing die? What bushing? How about a mandrel?

 

[ReaperDriver]

What kind of dies and sizing process? Are you using a bushing die? What bushing? How about a mandrel?

Redding Type S- Bushing dies. I full length size to bump the shoulder .002 under fired case. Neck bushing is a .291 for the gas gun .260. I have the usual expander button in the FL sizing die stem. No mandrels yet, but I just ordered a set of Wilson Mandrel expander dies to uniform the inside of the necks/case mouths. So hopefully that addresses the issue.

One thing that I'm seeing is the fired necks are still very tight. My understanding is a fired neck should slide right over a seated bullet as a test. But my fired cases still have the necks very tight. So I assume it must be a very tight chamber.

I'm just mainly trying to figure out of my issue is the donut and if that would cause the pressure signs I'm seeing.

 

[spife7980]

Clean it recently?

 

[spife7980]

The donut is a result of thicker shoulder material migrating into the neck. You can have donuts without having ever turned a neck.

Your bushing die should alleviate any donut issues though as it leaves the neck shoulder junction untouched as it resides in the dies bushing chamfer area so any thick part shouldn’t encroach too far inside the neck since it isn’t being pushed in.

 

[Steel head]

The donut is a result of thicker shoulder material migrating into the neck. You can have donuts without having ever turned a neck.

Your bushing die should alleviate any donut issues though as it leaves the neck shoulder junction in touched as it resides in the bushing chamfer so any thick part shouldn’t encroach too far inside the neck since it isn’t being pushed in.

This!
Heavy resizing and necking up brass to a bigger caliber are also culprits in getting donuts.

The bushing die with hide a mild donut but I feel can actually promote them at times as well if the bushing has to squeeze down the neck excessively.

 

[whatsupdoc]

The donut is a result of thicker shoulder material migrating into the neck. You can have donuts without having ever turned a neck.

Your bushing die should alleviate any donut issues though as it leaves the neck shoulder junction untouched as it resides in the dies bushing chamfer area so any thick part shouldn’t encroach too far inside the neck since it isn’t being pushed in.

^ This.


Donuts are a pain in the ass. I have found that using a standard expander button pulled up through the neck
seems to iron them out better than a mandrel pushed into the neck.

If you are using a mandrel you can make multiple passes to IRON out the doughnut, this seems to be
the easiest way to reduce the doughnut and you will need pin gauges to verify.

Another way is to ream the doughnut out, RCBS makes case neck turner pilot reamers that may or may not work depending
on the neck inside diameter of your brass. On my good brass if the doughnut gets too thick I resize then push a mandrel through
and use a chucking reamer of the exact neck inside diameter to cut out the doughnut.

If possible the best solution is to seat the bullet long so it does not make contact with the doughnut.

 

[Ironman308]

Take a loaded round and lay a bullet next to it with the tip of the bullets even. If the boat tail is at or forward of the shoulder neck junction then the dounut should not affect the round. If your seating deep then it can become an issue.

 

[mtang45]

I would be concerned that the necks of the fired cases are not expanding and is likely the source of the higher pressure. I'd find the reason for that rather than the donut.

 

[eschafer]

Are dounuts also a problem when using a Lee Collet neck-sizing die? My routine has now eliminated a sizing die with expander and gone to minimal shoulder set back with Redding Body Die then Lee Collet neck sizing die....

 

[Steel head]

Are dounuts also a problem when using a Lee Collet neck-sizing die? My routine has now eliminated a sizing die with expander and gone to minimal shoulder set back with Redding Body Die then Lee Collet neck sizing die....

Since I started using them I never have had any donuts but at the same same time I’m a lot more careful about other causes of donuts as well.

 

[2aBaC̶a̶]

Pin guages and an inside neck reamer.

Pin guages to know exatly what your inside dimentions are.

Forster can make a custom sized reamer so you can control how much it takes off by using different bushings.

 

[ReaperDriver]

Clean it recently?

Yep. And borescoped to make sure I'm not getting any carbon ring buildup.

 

[ReaperDriver]

The donut is a result of thicker shoulder material migrating into the neck. You can have donuts without having ever turned a neck.

Your bushing die should alleviate any donut issues though as it leaves the neck shoulder junction untouched as it resides in the dies bushing chamfer area so any thick part shouldn’t encroach too far inside the neck since it isn’t being pushed in.

I've not ever turned a neck. It could be that maybe I'm not sizing far enough down the neck and there is some thickness starting right at the line where the bushing stops. I have not been sizing all the way down to the shoulder and instead leaving a tiny bit of the neck unsized. Supposedly it was a trick that BR shooters did to get better neck tension or something.

My plan is to run it through a sizing mandrel and get the necks more uniform and then possibly turn them if the neck thickness is excessive.

 

[ReaperDriver]

Take a loaded round and lay a bullet next to it with the tip of the bullets even. If the boat tail is at or forward of the shoulder neck junction then the dounut should not affect the round. If your seating deep then it can become an issue.

I think this may be the issue - i.e. seating deep. On my .260 AI-AT - I seat 140 Hybrids at 2.950-2.955 because the AI mags are long. With the new gas gun, I'm mag length limited to about 2.840 with 130 Berger AR Hybrids. With the 123 Scenars I'm jam limited to 2.839 with the way the chamber is cut. So both things are driving me to a fairly deep seating depth. I'm going to try the trick with laying a bullet next to a loaded round and see where the BT falls. Thanks for that tip.

 

[ReaperDriver]

I would be concerned that the necks of the fired cases are not expanding and is likely the source of the higher pressure. I'd find the reason for that rather than the donut.

Yeah, this one is baffling to me as well. I assumed it was a chamber tightness issue. But am now thinking it is more of a neck thickness issue. I'm going to scope the chamber again it in a bit to make sure there isn't some buildup in the chamber I'm missing.

 

[DaveM]

Donuts in your brass should not be causing any kind of pressure problems. That’s not how it works.
Donuts form at the neck/shoulder junction on the inside of the case as the brass flows up with repeated firing. They will cause a very slight stricture in the case neck, but not enough to increase pressure when firing the shot.
Donut problems manifest as loaded rounds the will not fully chamber or require excessive force to chamber. When the full diameter of the bullet is seated deep enough to contact the donut it gets pushed to the outside of the neck creating a false shoulder basically. If you are careful to seat your bullets far enough out, you can prevent the full diameter from getting that deep and you’ll never know you have a donut. If you must seat bullets that deep, you would have to turn and inside ream your necks to remove the donut. Also, using an expander button on the downstroke of your press during sizing will cause the donut to drag on the expander likely stretching your case neck and altering your shoulder angle a few degrees.

Look elsewhere for your excess pressure problem.

 

[ReaperDriver]

Here are the loaded bullets with a bullet next to it for depth comparison. I'm stuck with seating about 2.840ish OAL due to the ACS mag lengths. Other hide folks have said you can seat out to 2.60-2.70 in those mags - but if I go much over 2.845 the tip is sticking over the lip of the mag.

123 Scenars ^^

130 Berger AR hybrids ^^

 

[ReaperDriver]

Donuts in your brass should not be causing any kind of pressure problems. That’s not how it works.
Donuts form at the neck/shoulder junction on the inside of the case as the brass flows up with repeated firing. They will cause a very slight stricture in the case neck, but not enough to increase pressure when firing the shot.
Donut problems manifest as loaded rounds the will not fully chamber or require excessive force to chamber. When the full diameter of the bullet is seated deep enough to contact the donut it gets pushed to the outside of the neck creating a false shoulder basically. If you are careful to seat your bullets far enough out, you can prevent the full diameter from getting that deep and you’ll never know you have a donut. If you must seat bullets that deep, you would have to turn and inside ream your necks to remove the donut. Also, using an expander button on the downstroke of your press during sizing will cause the donut to drag on the expander likely stretching your case neck and altering your shoulder angle a few degrees.

Look elsewhere for your excess pressure problem.

OK, fair enough. Any other suggestions to investigate? I'm pretty confident it's not a Headspace issue - I've been meticulous to measure fired cases from that chamber with a Hornady HS gauge and then FL size and shoulder bump to about .002 under. I'm running a JP High pressure bolt headspaced to that barrel and also running a heavy JP VMOS carrier with a SCS system as well. I've tuned the gas port to where it will just cycle nicely. Velocities are not excessive and in my load development I've been in the 2780 to 2850 range and still get pretty obvious swipe even at the low end. The other obvious sign of pressure is that some of the case heads have expanded more than what I've understood to be the norm - so that's un-good.

The biggest thing I'm noticing is the neck diameter AFTER firing is not much different than a loaded round. So it could be the necks are just too thick with a tight match chamber. We are trying an experiment now to turn the necks down and see if that helps. Hopefully I'll get to shoot them in the next couple of days to see if that's the issue.

 

[DaveM]

I think as long as you’re not getting deep ejector plunger marks in your cases, you’re fine.

Whose brass are you using?

Depending on how your gas system is timed, extraction and ejection upon firing is a pretty violent action. So, I wouldn’t expect pristine brass the to be the result. if all you’re getting is some ejector swipe, I‘d just run with it.

Based on the photos, if you had donuts in your cases, they would absolutly be causing chambering issues. You should be able to push your bolt carrier into battery by hand with the upper and lower separated. Open your rifle, and try it. Chamber a round by using no more force than a few fingers pushing on the back of your bolt carrier.

You don’t want to neck turn. It’s extremely labor intensive even with the right tools.

 

[Cardboard Assassin]

OK, fair enough. Any other suggestions to investigate? I'm pretty confident it's not a Headspace issue - I've been meticulous to measure fired cases from that chamber with a Hornady HS gauge and then FL size and shoulder bump to about .002 under. I'm running a JP High pressure bolt headspaced to that barrel and also running a heavy JP VMOS carrier with a SCS system as well. I've tuned the gas port to where it will just cycle nicely. Velocities are not excessive and in my load development I've been in the 2780 to 2850 range and still get pretty obvious swipe even at the low end. The other obvious sign of pressure is that some of the case heads have expanded more than what I've understood to be the norm - so that's un-good.

The biggest thing I'm noticing is the neck diameter AFTER firing is not much different than a loaded round. So it could be the necks are just too thick with a tight match chamber. We are trying an experiment now to turn the necks down and see if that helps. Hopefully I'll get to shoot them in the next couple of days to see if that's the issue.

That makes sense to me, maybe for comparisons sake its worth picking up a box of regular ammo (with new brass) and measuring the diameter of the outside of the neck before and after firing.

This could help in a few ways, you could see if the outside neck measurement after firing is the same as the brass you are having trouble, you could see if a bullet drop in easily into the fired cases (they should) and depending on what type of measuring equipment you have you could measure the thickness of the neck walls.

PS, Ive read lots about doughnuts here on the Hide but I don't think I have ever experienced any. There is lots of good info here. I use a Lee Collet die & Redding body die which from what I have read has less issues with doughnuts than bushing dies.

Are doughnuts ever visible? Does anyone have a picture?

 

[ma smith]

+1 Get a box of Berger 130 OTM in 260 rem

 

[Cardboard Assassin]

Yeah, this one is baffling to me as well. I assumed it was a chamber tightness issue. But am now thinking it is more of a neck thickness issue. I'm going to scope the chamber again it in a bit to make sure there isn't some buildup in the chamber I'm missing.

From what I am reading it is most likely a component of brass flow making the neck of the cartridge thicker.

If the neck walls get thick enough there is not enough room for them to expand sufficiently to cleanly "release" the bullet when fired (as they did before this issue started occuring) so that would result in higher pressure.

I guess what I am trying to say is that when fired a case should expand (which will aid in releasing the bullet) then contract a little (but still larger than its original size which is why a bullet will now drop into the fired case) so it can be ejected but your necks are now fatter from brass flow and don't have sufficient clearance to expand.

 

[Cardboard Assassin]

I've not ever turned a neck. It could be that maybe I'm not sizing far enough down the neck and there is some thickness starting right at the line where the bushing stops. I have not been sizing all the way down to the shoulder and instead leaving a tiny bit of the neck unsized. Supposedly it was a trick that BR shooters did to get better neck tension or something.

My plan is to run it through a sizing mandrel and get the necks more uniform and then possibly turn them if the neck thickness is excessive.

I just learned about that this week.

I am looking for some new dies and I was reading Orkans experiences with the SAC dies, he mentioned in there about what you describe.

The SAC dies dont neck size the full length of the neck, they leave a little at the base, the theory being that little bit which is untouched will help to centre the round perfectly when it goes back in the same chamber.

 

[DaveM]

You guys are all really starting to overthink this. You’re inserting variables and scenarios that just don’t matter.

Brass donuts happen on many different cartidges. You can fight with them, or work around them. Working around them is easy provided you know what they actually are. Now you do.

You’re shooting a gas gun. They are not gentle on brass. Don’t expect perfect, pristine brass to come out of it.

You‘re discussing reloading processes and steps normally reserved for benchrest levels of detail. That type of stuff requires massive amounts of time and money. One thing you must accept is there are no free lunches when it comes to reloading. Every new step or process you introduce into your reloading process is likely going to have an effect on another step or is going to yield unintended consequences.

Keep it simple. For PRS with a gas gun, load ammo that will shoot consistent 1/2 MOA groups and spend more time practicing good fundamentals.

 

[phlegethon]

Are doughnuts ever visible? Does anyone have a picture?

case neck donuts – Midsouth Shooters Blog

Posts about case neck donuts written by msshootersadmin

www.mssblog.com

 

[Cardboard Assassin]

case neck donuts – Midsouth Shooters Blog

Posts about case neck donuts written by msshootersadmin

www.mssblog.com

Thank you. A picture is worth a 1000 words and all that.

The "doughnut" was in the shiny area at the neck / shoulder junction but was removed (hence the shininess). I'm guessing that before it was removed the actual issue (increased thickness) was so subtle it probably couldn't have been seen with the naked eye (several thousandths).

From what the OP describes (The reason I suspect the "donut" is because when you slide a bullet into a fired neck, it feels like it hits a stop right around the shoulder/neck junction and my shooting partner said "It feels like a donut") this would explain it perfectly.

There is some great info in the article too.

 

[Cardboard Assassin]

Shamelessly stolen from said article to make it easier for anyone who stumbles across this thread (as mentioned previously the shiny area is what was removed to correct the doughnut issue):

 

[2aBaC̶a̶]

Here are the loaded bullets with a bullet next to it for depth comparison. I'm stuck with seating about 2.840ish OAL due to the ACS mag lengths. Other hide folks have said you can seat out to 2.60-2.70 in those mags - but if I go much over 2.845 the tip is sticking over the lip of the mag.

View attachment 7621382
123 Scenars ^^

View attachment 7621384
130 Berger AR hybrids ^^

Is it just me or does the case mouth look flared and almost peened over?

 

[Cardboard Assassin]

Is it just me or does the case mouth look flared and almost peened over?

It looks a little flared for sure

 

[NH4X]

case neck donuts – Midsouth Shooters Blog

Posts about case neck donuts written by msshootersadmin

www.mssblog.com

Internet winner of the day............thx for finding and posting...........for those that don't know,Glenn's books are worth what you pay for them.

 

[chevy_man]

Here are the loaded bullets with a bullet next to it for depth comparison. I'm stuck with seating about 2.840ish OAL due to the ACS mag lengths. Other hide folks have said you can seat out to 2.60-2.70 in those mags - but if I go much over 2.845 the tip is sticking over the lip of the mag.

View attachment 7621382
123 Scenars ^^

View attachment 7621384
130 Berger AR hybrids ^^

You can see the donut on the neck.


Neck turn the brass 1x and I'll bet your issue stops. Tight necked chamber, and bushing die that's not bottoming on the neck.

Not uncommon with bushing dies. A standard full length die can sometimes smooth them back out.

 

[ReaperDriver]

I think as long as you’re not getting deep ejector plunger marks in your cases, you’re fine.

Whose brass are you using?

Depending on how your gas system is timed, extraction and ejection upon firing is a pretty violent action. So, I wouldn’t expect pristine brass the to be the result. if all you’re getting is some ejector swipe, I‘d just run with it.

Based on the photos, if you had donuts in your cases, they would absolutly be causing chambering issues. You should be able to push your bolt carrier into battery by hand with the upper and lower separated. Open your rifle, and try it. Chamber a round by using no more force than a few fingers pushing on the back of your bolt carrier.

You don’t want to neck turn. It’s extremely labor intensive even with the right tools.

I'm using Lapua .260 brass. And yes I'm getting deep ejector plunger marks. Even with the gas turned off. With the gas on, at the higher end of my OCW tests, the bolt then shears off the plunger mark when the bolt rotates. I'll try to get some pics.....

 

[ReaperDriver]

That makes sense to me, maybe for comparisons sake its worth picking up a box of regular ammo (with new brass) and measuring the diameter of the outside of the neck before and after firing.

This could help in a few ways, you could see if the outside neck measurement after firing is the same as the brass you are having trouble, you could see if a bullet drop in easily into the fired cases (they should) and depending on what type of measuring equipment you have you could measure the thickness of the neck walls.

PS, Ive read lots about doughnuts here on the Hide but I don't think I have ever experienced any. There is lots of good info here. I use a Lee Collet die & Redding body die which from what I have read has less issues with doughnuts than bushing dies.

Are doughnuts ever visible? Does anyone have a picture?

Reference the red bolded statement.....No a fired bullet will not slide into a fired case mouth as stated in the OP. This is what started me down the whole "donut" rabbit hole in the first place.

 

[ReaperDriver]

You can see the donut on the neck.


Neck turn the brass 1x and I'll bet your issue stops. Tight necked chamber, and bushing die that's not bottoming on the neck.

Not uncommon with bushing dies. A standard full length die can sometimes smooth them back out.

Yeah, my FL bushing die will not size the entire neck. I think I'll go back to my neck only bushing die (Redding also) and size all the way to the neck/shoulder juncture.

 

[Cardboard Assassin]

Reference the red bolded statement.....No a fired bullet will not slide into a fired case mouth as stated in the OP. This is what started me down the whole "donut" rabbit hole in the first place.

I was referring to the fired brass from factory ammo if you buy some and shoot it, not the brass you already have / are having trouble with.

 

[ReaperDriver]

I was referring to the fired brass from factory ammo if you buy some and shoot it, not the brass you already have / are having trouble with.

Ah, gotcha. The problem is obviously trying to find a box of Berger 130 OTMs with Lapua brass in this current market. It could be months before I get lucky enough to score one.

 

[308sako]

Been watching this thread with interest, so waiting to hear what comes of it.

 

[ReaperDriver]

Been watching this thread with interest, so waiting to hear what comes of it.

You know exactly what came of it..... you were there.

 

[2aBaC̶a̶]

Well did you figure it out?

 

[ReaperDriver]

Soooo.... the answer was..... wait for it.... Wait for it...... Neck thickness. @308sako was kind enough to neck turn some of the offending Lapua brass down a bit given I didn't have the tools on hand to be able to run a test. First he did a mandrel to uniform the inside of the necks and then used a Sinclair neck turning tool to cut down the neck wall a bit. Prior to the neck turning, loaded Lapua .260 cases were in the .298-.299 range. After neck turning - the loaded necks were in the .2935 to .2940 range. We did a quick test today with the neck turned cases shooting the same load that had given lots of pressure. Pressure was essentially gone. No swipe, nice rounded primers. It turns out the chamber is just cut so tight that there didn't appear to be room for the neck to expand on ignition and that was causing a pressure spike as the bullet was being held there by the neck. Not sure if that is the technical way to describe it - but that's my understanding.

So the problem appears to be gone (halle-FREAKIN-lejujah, but now I have to turn all the rest of my Lapua brass.

 

[KnowNothing256]

I understand and agree that turning your necks is the easiest fix at this point, but I’d be pissed about that chamber. Lapua brass is top of the line and should function well out of the box.

Unless you ordered/bought a “custom” or “match” chamber, in which case ok, yeah, stands to reason it’d be tight.

 

[ReaperDriver]

It was not a custom barrel but it was definitely expected to be a “match” barrel. I’m not complaining, I knew it was going to be tight to achieve the accuracy that is claimed. But I sorta was unprepared for Lapua to end up being TOO tight and require that level of prep to make it shoot well. I’ve probably toasted a half box of brass in 3 loadings even when starting low.

 

[milboltnut]

get this.... 12 cases sized and one out of the 12 does not have a donut.

cheap way out? Forster special order reamer.... two week wait. Ebay reamer, if you can find the diameter you need, I did, delivered in less than a week. Redding says it's better to use a reaming die. Can find some on ebay.

 

[2aBaC̶a̶]

I got a custom Forster reamer in .3065 for .308. I can control how much is removed by using different bushings.

 

[NoDopes]

I think most shooters agree that using a button expander when dealing with donuts will lead to higher final runouts.
Mandrel and/or reamer will be better.

 

[milboltnut]

2aBaCa

when you use different size bushings.... do you see a improvement in accuracy?

 

[milboltnut]

I think most shooters agree that using a button expander when dealing with donuts will lead to higher final runouts.
Mandrel and/or reamer will be better.

For sure.... also I tried last night to size with the expander ball then expander mandrel.. and the donuts still were there. Just ordered a reamer.

 

[flyright]

From another thread:

"When I began using the honed die and mandrel method, my results were great. However, I am beginning to see the internal donut more and more with brass sized this way. I plan to do a couple of control groups of once fired brass using the honed die with expander ball installed and with and without using the mandrel after.

A friend of mine has experienced the same and has since went back to just using the standard expander ball, skipping the mandrel, and his neck size/seat forces are very consistent now. He believes the donut problem has resolved as well. Just my .03."

I have found that once the donut has formed, a pass through a die with the expander installed, will NOT remove it.

 

[NoDopes]

It is probably a little easier to remove donut with force if you are annealing with perhaps a little less spring-back.