case neck donuts

[dieselten]

I started using Redding type S bushing sizer dies about 2 years ago when reloading for 6BR, 6x47L, and 6.5-284. I only use Lapua brass. I did not load these calibers previously so I have no comparison to other dies. Anyway, I would start seeing erratic grouping after about 4-5 reloads and I tried everything to fix it. Then I read a post here about donuts so I checked. Sure enough, I had them. I got in there delicately with a needle file to make sure I did not touch the bullet seating area in the case neck. I would remove brass until a bullet would slip into a fired case. OK, so I thought my problem was solved. Nope, after the next firing it was back again. I am full sizing with a .001-.002 shoulder setback. Expander ball removed. Bushings are selected for about .002 tension. I run the bushing almost all the way down as the die will allow, leaving about .010.

My questions -

Are the donuts caused by the bushing dies?

If I switch to a custom neck honed full size die without bushings and use the expander ball, will that keep donuts from forming?

 

[Leaddog]

Good question. Are you neck turning? If you are, are you slightly cutting into the shoulder as you should be?

I run the same setup as you in .308 and have not experienced that problem. I do turn my necks just slightly (.0005) kissing the shoulder. That's all I skim to make my Lapua brass consistent.

 

[CanusLatransSnpr]

I have read that the use of bushing dies can result in donuts. I use a Redding Type S neck bushing die for my .243 Win and haven't experienced any donuts yet. However, I'm only on my third firing on this set of brass. Also, if only .010" of neck is all that is left unsized, you're doing good. My bushing neck die leaves far more than that unsized and I have it adjusted properly too. Just the nature of the beast I guess?

Mike

 

[dieselten]

I turned the necks on my 6x47 but the others are not touched. Cutting in to the shoulder might help. I do not think I am getting the bushing down to .010 from the shoulder, I am adjusting the die to .010 from full bottom out bushing adjustment. It looks like there is about .050 or more of neck unsized on my cases.

I use the bushings on a .243 also and have not had problems after 4 reloads. I think it might only come in to play with close neck tolerance chambers.

 

[lpreddick]

internal reaming with a wilson trimmer setup is my current procedure.same problem here. my gunsmith tells me they had donuts 50+ years ago before bushings. a bushing may hasten the development while neck turning onto shoulder may slow their appearance. an expander ball will not "iron out" an established donut. my steel neck expanders will not either. i pushed a flatbased bullet thru a donut in some 6.5-284 norma brass and the donut COMPRESSED the bullet jacket to the point it would push thru the donut and stop where the compression stoped. inside neck reamers will remove it nicely and you can really feel just how hard this ring of brass can be. hand turning the wilson rreamers can be very difficult. now, i was going to post the following: i borescoped some brass with and without donuts...interesting. the slope of the shoulder transitioning to the neck is very sharp. with a donut, there is a ridge in the neck EXACTLY where this slope transitions to neck. this ring of brass is BELOW the lowest point that the bushing reaches externally. the ring(donut) appears to be brass that has "flowed" out of the shoulder and piled up in the base of the neck. i havenot seen any evidence that a donut is a problem UNLESS you seat a bullet thru it, in which case the very tight grip on the bullet could result in high pressures, crazy runout and who knows what results. how soon does one appear? are some cases more prone to forming donuts ? heating brass to high temps SOFTENS it but this brass ring is very hard. is this work hardening at it's worst? as usual i have more questions than answers.

 

[Scott Harris]

Lapua brass is thicker in the shoulder than in the neck. Not sure why they do that, but, like you, I get donuts pretty quick in my 243WIN brass. I'm pretty sure this is the result of brass flowing from the shoulder to the neck. Tried a few methods, but the best, by far is to neck turn liberally into the shoulder. If you have a turning blade with the correct shoulder angle on it, then you can cut pretty far up the shoulder safely and never have to worry about donuts for the life of the brass.

 

[JohnD]

Not to hi-jack here but what is the best method to identify a donut? Should
a bullet slide easily into a fired case?

Thanks, John.

 

[jlow]

I see donuts pretty often even in once fired 308 win brass and yes I do neck turn. I am pretty sure they are caused by case material from the shoulders moving into the shoulder neck junction. I don’t think one can blame the Redding Type S busing die as they are made to only size the forward part of the neck leaving an area between the size area and the shoulder/neck junction unsized. My theory is that they do this on purpose so that no donut area will be sized even smaller and cause even more of a problem – but this is only my own pet theory.

The problem with donuts is that they cause uneven seating pressure, neck tension, and so uneven MV. The best way I have found to detect them is to push in a K&M carbide cutting pilot by hand, it slides in smoothly after the brass has been expanded by the K&M case neck expanding mandrel and stops dead when it encounters the donut. I remove it by chucking the carbide cutting pilot into a drill, insert the case into the pilot until it stops and cut it out using a motorized action on the pilot.

Not an expert but this is my experience.

 

[dennisinaz]

I do not claim to be an expert on this but I will share my remedies. I encountered donuts when making 260 brass from 308 lapua. I used a .250" chucking reamer with the case chucked in my lathe. I spun it about 125 rpm. I would slide the reamer in by hand and use my thumb as pressure to the side of the neck and angle the reamer slightly to cut out the donut. I got very efficient at it and it does a good job.

To prevent donuts, take a health cut into the shoulder- at least 4 thousandths maybe more when neck turning. The shoulder is probably at least . 018" thick. When I figured this out, I would neck turn while my brass was .308 and then size down- this would put the turned portion well into the neck. A final light cut <.001" was taken after sizing to 260.

Bushing dies are worse because they don't size the whole neck.

 

[FroggyOne2]

All my load development is done with the bullet seated above the area that would be concern for the dreaded "D" area.

 

[Catfish]

The dounut problem is more pronouanced with hot rod calibers and I shoot several of them. With some I have to inside neck turn every time I load them, especially with hotter loads. Just get an inside neck turner and your problems will be gone.

 

[areaone]

Froggy, what area do you seat above, the shoulder?