Neck dougnuts

[dannywayoflife]

I keep hearing the term dougnuts with reference to cases but don't fully understand what they are and if I have them how to get rid? Also how can you tell if you have them?

 

Thanks guys

 

 

Danny

[DaveT]

If the bullet won't pass through the neck of a fired (unsized) case then you probably have a donut...could also be held back by burrs on the neck though so chamfer and recheck.

 

As far as I am aware it is caused either by the expander ball dragging some brass up to the shoulder/neck junction so causing a minute ring of brass to form up inside the case at that point OR can also be created when neck turning if you don't take the cut slightly into the shoulder and leave a ridge which transfers to the INSIDE of the case upon firing.

 

If your bullet does not seat deeply enough to touch the donut then no worries...otherwise you will need to junk the case or inside ream the donut away.

[The Gun Pimp]

The easiest way to form a doughnut is when you neck up a case - say 6.5-284 to a straight 284 or a 243 to a 260.

 

After running in the up-sizing mandrel, there will be a small radius formed at the base of the neck - rather than a sharp angle.

 

Your rifle's chamber of course has a sharp angle at this point so, when you chamber the round and fire it, the 'angle' is forced to the inside of the neck - forming the doughnut.

[Laurie]

The main doughnut issue for most target shooters arises from necking up a parent case to the desired version - so .220 Russian to 6PPC; .22-250 Rem to 6XC, 6.5mm Hornady Creedmoor and various 6mm widcats; .243 Win to .260 Rem (no longer necessary now that Lapua makes 260 brass); and the practice that currently most commonly affects F-Class shooters, 6.5-284 Norma to .284 Win / 7mm Shehane as well as various minor changes to WSM brass to get to the desired final form.

 

By changing neck diameter, the original factory shoulder / neck junction point becomes part of the neck, right at the bottom and even when neck-turning of the pre-expanded case is done including a shallow cut into the shoulder, the alteration nearly always creates a narrow internal ring at the bottom of the neck. It's more of a crease than a ring / doughnut as it's so narrow. It can also in theory, but rarely does, form in an unmodified case as brass flows forward under the effects of the firing / sizing cycle. In either event, the existence of a doughnut ring is easily felt on seating a bullet in a case sized to give light to moderate neck-tension. The bottom of the bullet shank reaches the doughnut and the resistance to seating as felt through the press handle rises appreciably.

 

As Dave T says, there are basically three cures - don't adopt a cartridge that is either prone to the problem or needs another basic case reformed; throat the rifle so the bullet is always seated above the doughnut ring; use an inside neck-reamer to cut it out. If you don't and seat bullets through the doughnut, you're unlikely to ever get the rifle / cartridge to fulfil their true potential.

 

With most, the vast majority in fact, of factory cartridges, .223; 308, 243, etc and good brass it's simply never likely to arise.

[jcampbellsmith]

Laurie

 

I'm not sure I agree with you. I've doughnuts in 6XC (Norma) and 260 Rem (Nosler) brass. These cases haven't been necked up or down. They have been full length resized. I'm pretty sure some of 6XC doughnuts were formed during resizing (or got more pronounced). Both chambers will take factory ammo and have 3-4 thou neck clearance.

 

My sense is folk that don't look for doughnuts don't find them. On the Nosler brass I noticed some inconsistencies in velocity on the fifth firing and the checked using a bullet inserted into the fired cases.

 

I'm unsure how best to address the issue, but one tack on the 260 Rem is to move away from the 140 gr A-Max to the lighter 123 gr A-Max and make sure the bullet is seated above the doughnut.

 

Regards

 

JCS

[dannywayoflife]

Thanks for the replys gents! Everyday is a school day! So the general thinking is unless I'm forming cases (which I'm not I run 308&243) I shouldn't have problems?

[gbal]

Correct,you should have no worries,Danny,with standard 243 and 308 brass (just don't neck up the 243 to 308!)

gbal

[dannywayoflife]

That's what I wanted to hear! Cheers chap

[JSC]

Laurie

 

I'm not sure I agree with you. I've doughnuts in 6XC (Norma) and 260 Rem (Nosler) brass. These cases haven't been necked up or down. They have been full length resized. I'm pretty sure some of 6XC doughnuts were formed during resizing (or got more pronounced). Both chambers will take factory ammo and have 3-4 thou neck clearance.

 

My sense is folk that don't look for doughnuts don't find them. On the Nosler brass I noticed some inconsistencies in velocity on the fifth firing and the checked using a bullet inserted into the fired cases.

 

I'm unsure how best to address the issue, but one tack on the 260 Rem is to move away from the 140 gr A-Max to the lighter 123 gr A-Max and make sure the bullet is seated above the doughnut.

 

Regards

 

JCS

 

Regardless of whether you personally necked it, some factory produced brass such as Norma 6XC is prone to doughnutting after a few firing/resize cycles. An inside reamer is the answer unless you want to change the bullet.

[DaveT]

Laurie

 

I'm not sure I agree with you. I've doughnuts in 6XC (Norma) and 260 Rem (Nosler) brass. These cases haven't been necked up or down. They have been full length resized. I'm pretty sure some of 6XC doughnuts were formed during resizing (or got more pronounced). Both chambers will take factory ammo and have 3-4 thou neck clearance.

 

My sense is folk that don't look for doughnuts don't find them. On the Nosler brass I noticed some inconsistencies in velocity on the fifth firing and the checked using a bullet inserted into the fired cases.

 

I'm unsure how best to address the issue, but one tack on the 260 Rem is to move away from the 140 gr A-Max to the lighter 123 gr A-Max and make sure the bullet is seated above the doughnut.

 

Regards

 

JCS

I also got doughnuts on Nosler 260 brass...never happened since I changed to Lapua though...weird!

[Laurie]

I suspect this is a production issue. I never had any doughnut issues on my Norma 6XC brass when I used this chambering. The XC was nearly notorious for variations in brass quality depending on era with (I think) three major 'marks' of brass recognised and regarded as good / acceptable / bl**dy awful by American 6XC aficionados.

 

I'll be doing a lot of playing around with 260 Rem brass in 2015 as a major project to see just how much (or little?) brass quality and preparation affects consistency, and it'll be interesting to see whether the doughnut issue arises - .260 Rem seems to be one of the few designs where it does appear in factory form. My first go at getting good 260R cases some years back involved necking-up Lapua .243 in the days before I became addicted to neck turners (cheaper, barely, than cocaine!) and OMG it DID produce doughnuts - they even showed on the outside of the neck as a thin bright line.

 

So, I've got this stuff still, plus proper Lapua 260 - early lot and maybe the best out of the box brass I've ever measured BR and 220 Russian apart - Winchester 7mm-08 to neck down (American .260 Rem fan S.O.P. to get decent brass before Lapua made it), new yellow/green bag Remington, factory Remington and Federal sporting ammo and I think one other but can't remember what as starting points. The one glaring omission is Norma, but I'm not completely bankrupt yet and want to stay that way!

 

I'll also have a go at necking Lapua .308 Win 'Palma' small primer brass down to .260 - widely done by Australian precision shooters for 260 and 7mm-08 and described as being well worth the effort.

[Ronin]

Simple way of avoiding donuts is to undercut the neck / shoulder junction when your neck turning - cut in by .015 - .025" - (its easier to see rather than measure)

 

 

 

Right hand case - necked up 6.5x284 Lapua case - necked up to .284" then turned on K&M to .012' wall thickness.

 

You can see the obvious undercut at the shoulder neck union.

 

Left hand case - fire formed .284 Shehane - the undercut line is still visible on the shoulder but the brass has flowed in, preventing the formation of a donut - no need for internal trimming.

[jcampbellsmith]

Andy. Thanks. I've started to neck turn some of my cases, just giving them a skim and trying to make a witness mark at the neck/shoulder junction. Regards JCS

[jcampbellsmith]

I suspect this is a production issue. I never had any doughnut issues on my Norma 6XC brass when I used this chambering. The XC was nearly notorious for variations in brass quality depending on era with (I think) three major 'marks' of brass recognised and regarded as good / acceptable / bl**dy awful by American 6XC aficionados.....

 

Laurie. Thanks. That's very interesting. The majority of my 6XC brass is from one vintage lot dating from when 6XCs first appeared in the UK. However I do now have ten fired cases from Norma Oryx factory ammunition. I think I'll work away with what I've got. It was going quite well this afternoon with some 105 gr Scenars.

 

Best regards

 

JCS