Bullet bearing surface, seating depth, doughnuts.....

[Alex Wheeler]

A lot of times we get caught up with keeping the bearing surface above the neck/shoulder junction. I have read that it is "critical to accuracy" to keep the bullet above the doughnut. Well, I say bs. Well, not always. So a doughnut is a thickened ring that forms at the neck/shoulder junction. It is only a problem if it contacts the bullet. Why? Because we cant control neck tension in this area. Even without a formed doughnut you dont want a bullet to contact the neck/shoulder junction. With a bushing or even a fl die with a radius in this area we are ok. The other issue is bullets pressure rings. If we have a bullet with a pressure ring it can act as an expander when seating the bullet. Its ok if the pressure ring stays in the sized part of the neck because neck tension will be maintained over the ring. If the bullet is seated deep enough that the pressure ring goes through the sized part of the neck, we have reduced neck tension to something around .0005-.001". Some rifles may shoot like this but I would rather have control over neck tension. So, its my opinion that if your bullet does not have a pressure ring and you use a bushing die so the doughnut doesnt contact the bullet you will not see any accuracy issues from seating the bullet past the neck shoulder junction.

 

[Northridge]

I would agree Alex....

Shawn williams

 

[ShootDots]

Alex, I agree in principle. However, I will give you an example, then ask a question. I have a 30-06A.I. For whatever reason that brass develops the worst doughnuts of any case I have ever seen. I have cut out the doughnuts often on the brass. They develop so quickly, a mandrel, just after a few firings, will not pass thru! QUESTION: What if I never cut out the doughnuts and simply allowed them to continue growing. Would they not inhibit "proper / consistent" combustion thru that point, possibly to the point of disturbing accuracy?

 

[Alex Wheeler]

Your asking if the doughnut would affect the gas flow? Assuming they were bad, say .005" that would be roughly a 3% reduction in neck id. Negligible Id think. And thats assuming there was some with no doughnut, if they all had doughnuts that were remotely consistent then there error would be even less.

Its not just principal, the best dasher barrel I had was .090 fb and the shank of a Berger was through the neck. I did suffer loss of neck tension, which is why I contribute that barrel to liking Varget. 4895 and rl15 like more neck tension than I could achieve.

 

[ShootDots]

Your asking if the doughnut would affect the gas flow?

Yes Sir>>>if they get large enough and vary enough in the size of the restriction to that flow.

 

[Alex Wheeler]

I added to my post. I really doubt it, but anything in an extreme I suppose could have an effect. I did used to shoot a 260 ai and it had very bad doughnuts. I didnt seat the bullet into them but it would literally stop the bullet on the doughnut. I did not experience accuracy issues and this was on a br platform.

 

[ShootDots]

Your asking if the doughnut would affect the gas flow? Assuming they were bad, say .005" that would be roughly a 3% reduction in neck id. Negligible Id think. And thats assuming there was some with no doughnut, if they all had doughnuts that were remotely consistent then there error would be even less.

Its not just principal, the best dasher barrel I had was .090 fb and the shank of a Berger was through the neck. I did suffer loss of neck tension, which is why I contribute that barrel to liking Varget. 4895 and rl15 like more neck tension than I could achieve.

Some have less build up of brass in that area than others. However, in my opinion, they are all "bad". Thank you for your answer, I appreciate it.

 

[Alex Wheeler]

Some have less build up of brass in that area than others. However, in my opinion, they are all "bad". Thank you for your answer, I appreciate it.

Sure, anytime. My opinions are worth exactly what you paid for them

 

[BoydAllen]

What if you were to cut off a die, intentionally push the shoulder of a case back quite a bit, turn the resultant over-long neck back to the pushed back shoulder, and then expand the neck over your target diameter and then size the case with the correct FL die, set to produce a false shoulder in the correct location? What you would end up with it the top of the shoulder the same thickness as the neck. Doughnuts are merely the thicker material in the top of the shoulder that has been forced into the bottom of the neck by repeatedly pushing the shoulder back and reducing the diameter of the bodies of fired cases as they are FL sized. If the case thickness is the same at the top of the shoulder as it is in the neck... no doughnut. You can keep track of how fast you are likely to be developing doughnuts by how much and often you have to trim, to maintain the same case length.
Note: This has been severely edited to remove ramble, and scatter. It needed both.

 

[RonAKA]

So, its my opinion that if your bullet does not have a pressure ring and you use a bushing die so the doughnut doesnt contact the bullet you will not see any accuracy issues from seating the bullet past the neck shoulder junction.

I tend to agree. However, when I test the neck of a fired case with a bullet, I do have a donut at the neck shoulder junction in my 6BR, and I only partially resize the neck with a bushing die. And I don't turn the necks. I don't seat bullets anywhere near that deep, but I think if I did, there would be an increase in neck pullout force if I seated the bearing surface back behind the shoulder junction (and donut).

 

[Alex Wheeler]

You probably have a .2704" no turn? Too tight in my opinion. But I see your point. Thats a whole other subject but we have gotten way too tight with neck clearance and chamber clearances in general.

 

[Tim s]

First of all a donut usually occurs from improperly neck trimming, second, they often come up into the neck past the radius. Third, they can easily be removed rarely requiring a second cut.
At the end of the day, simply trim necks properly and this is all moot.

 

[Alex Wheeler]

First of all a donut usually occurs from improperly neck trimming, second, they often come up into the neck past the radius. Third, they can easily be removed rarely requiring a second cut.
At the end of the day, simply trim necks properly and this is all moot.

Doughnuts form from thicker shoulder brass flowing into the neck. This has nothing to do with trimming of the neck. If you mean turning the neck, this can help but if you shoot the case enough the brass flow will still form a doughnut eventually.

 

[Tim s]

Doughnuts form from thicker shoulder brass flowing into the neck. This has nothing to do with trimming of the neck. If you mean turning the neck, this can help but if you shoot the case enough the brass flow will still form a doughnut eventually.

Yes, my mistake, turning not trimming.
That said, they are most ften the case from a turning job that cuts short, that is to say above the neck/shoulder junction.
There was actually a comprehensive piece done years ago in Precision Shooting.
Now some of the boomers you may build, I've zero experience, however I cannot imagine the physics of a PPC case vary much.
The principle cause of donuts is when necks get turned short and over time the dimensional varience shifts from the outside to the inside of the neck.
This is a principle reason K&N started initially putting a radius on there tool to come into the shoulder, largely duplicated by many turning tools.
Once cut properly, no donuts to begin with or any time there after.
I have run a mandrel/reamer into cases with countless firings, just to check, and never cut brass inside a properly turned neck.

 

[Alex Wheeler]

Yes, my mistake, turning not trimming.
That said, they are most ften the case from a turning job that cuts short, that is to say above the neck/shoulder junction.
There was actually a comprehensive piece done years ago in Precision Shooting.
Now some of the boomers you may build, I've zero experience, however I cannot imagine the physics of a PPC case vary much.
The principle cause of donuts is when necks get turned short and over time the dimensional varience shifts from the outside to the inside of the neck.
This is a principle reason K&N started initially putting a radius on there tool to come into the shoulder, largely duplicated by many turning tools.
Once cut properly, no donuts to begin with or any time there after.
I have run a mandrel/reamer into cases with countless firings, just to check, and never cut brass inside a properly turned neck.

I dont disagree with you. That is one cause. However a doughnut can form in a case that has not been turned as well. Brass flow. Point I was trying to make is that there is nothing wrong with bullet shank exposed inside the case. Some of the stuff you read would make you think if you seat a bullet past the neck/shoulder junction the rifle wont shoot for beans.

 

[dmoran]

@Tim s
Like Alex, feel you partially right. And to add just a little more to Alex's replies, what happens in one cartridge and brand of brass, is not always what happens in others. So many variables, such as shoulder angles, wall thickness, hardness, etc., to say all will react as have your own in your cartridges and brands.
Good discussion....
Donovan

 

[3081FTR]

I dont disagree with you. That is one cause. However a doughnut can form in a case that has not been turned as well. Brass flow. Point I was trying to make is that there is nothing wrong with bullet shank exposed inside the case. Some of the stuff you read would make you think if you seat a bullet past the neck/shoulder junction the rifle wont shoot for beans.

Agree. Pretty much any config can be made to shoot but some designs require more understanding in order not to run into issues.
I've always viewed it as a rule of thumb. i.e. typically best to stay away from that area as you are more likely to have an issue if you are seating that deep.
One reason to stay away is it can be a pain to discern what the issue is and if a donut has formed.

I stumbled across donut issues in a no neck turn 6BR shooting 88 grn bergers. These are a long flat base varmint bullet. Had a good load and was up at the range with brass that was on its 3rd reload. Blanked a couple of primers, hmm that's weird. Later that evening I was reloading more and had a hell of a job getting the bullets to seat in at the correct depth, they would seat in and then pop up ~.006", others would be fine. Getting annoyed now ( ). While playing around trying to figure it all out I dropped a bullet into a case (can't recall exact circumstances now) and the bullet stopped right at the neck shoulder junction. The light bulb went on, donuts. Turns out my selected seating depth meant the flatbase bullet was ending up right on top of the donut. The blanked primers were due to the bullet being seated into the donut and the bullets that wouldn't seat I am pretty sure were ending up on the leading edge of the donut and hence sliding backout marginally.
The give aways were; load that had been good for some time started blanking primers on multi fired brass. Inability to hold the seating depth, the flat base ending up right at the neck shoulder junction and last but not least the bullet not sliding in past the neck shoulder junction.
I never had a donut reamer..I think I used an expander mandrel to pop the donut out and then once the 88s were used up I went to a different bullet to get away from that area and have never looked back.

PS - great posts and videos (other threads) - efforts much appreciated

 

[dkhunt14]

Most all of the bullets I shoot have pressure rings. Sometimes it is not a great amount, but some lots are .002 or more. I agree if the pressure ring is not in the sized part of the neck you will have tension problems. It would be like running game an expander through the neck. I like lots of tension. I shoot almost everything in the lands and I don't want the bullet moving when I close the bolt.

The thing I see, is if the throat is not long enough to let the bullet be seated out the donut area, is now you are taking up powder capacity. It seems I get more velocity without as much pressure by throating it out farther. I feel this is as important as being out the donut area for seating issues. Matt

 

[msinc]

Could I trouble one of you guys to clarify two things???? First, what exactly is a "blanked" primer??? I am having trouble connecting the dots between something wrong {guessing here} with a primer and case necks. Are you saying that the donut is moving the shoulder back {headspace} when the bullet is seated and the primer isn't igniting???? And second, how do you know or test for a "pressure ring" on a bullet???? dkhunt14, are you saying that there are bullets out there that have a .002" {two thousandths of an inch???} larger in diameter area on the bearing surface???? "Or more"?????....how much more?????
All my shooting life I have never knowingly had a problem with the "dread donut"...in fact, until I read Tony Boyer's book I had never even heard of such thing.
I do shoot several 30-06 AI rifles a good bit but have never had any issues. After hearing and reading so many guys hammering about this donut thing I even went so far as to make test mandrels on my lathe that are the exact size of the sized neck to see if there was any drag...none at all so far. This includes both untouched and outside neck turned brass. I am not normally associated with much good luck, could it be that I have just been lucky for the last 15 years and several thousand rounds or so????

 

[dkhunt14]

Could I trouble one of you guys to clarify two things???? First, what exactly is a "blanked" primer??? I am having trouble connecting the dots between something wrong {guessing here} with a primer and case necks. Are you saying that the donut is moving the shoulder back {headspace} when the bullet is seated and the primer isn't igniting???? And second, how do you know or test for a "pressure ring" on a bullet???? dkhunt14, are you saying that there are bullets out there that have a .002" {two thousandths of an inch???} larger in diameter area on the bearing surface???? "Or more"?????....how much more?????
All my shooting life I have never knowingly had a problem with the "dread donut"...in fact, until I read Tony Boyer's book I had never even heard of such thing.
I do shoot several 30-06 AI rifles a good bit but have never had any issues. After hearing and reading so many guys hammering about this donut thing I even went so far as to make test mandrels on my lathe that are the exact size of the sized neck to see if there was any drag...none at all so far. This includes both untouched and outside neck turned brass. I am not normally associated with much good luck, could it be that I have just been lucky for the last 15 years and several thousand rounds or so????

A blanked primer is when you punch a hole in one. Too much headspace can create a blanked primer. So if the donut is causing a shoulder setback when seating it can cause a blanked primer.

A pressure ring is at the back of the bullet, right where it ends or goes into a boat tail . Yes I have as much as .004 on some. It is usually about .002 average on my VLD's. It can be measured with a good micrometer. Matt