Donuts.

A

Alpheus

CGN Ultra frequent flyer
Rating - 100%
168   0   0
Location
Ottawa
I have them. Dammit. I was looking over my 6BR brass before I try my hand at annealing, and a bullet would not drop through unsized brass. Used my Redding neck gauge, yup, donuts. I use a Forster bushing die, and can see that the entire neck isn't resized by the bushing, even with the bushing set at minimal float. I assume this and my .272 neck are what caused them?

I understand that inside reaming can be used to remove them. I have a Forster handheld outside neck tuner, this page seems to show that the reamers for their standalone unit will fit the handheld turner. http://www.opticstalk.com/case-neck-donut_topic12628.html

Another possibility is using an expander to push the donut to the outside and then neck turn, slightly cutting into the shoulder. Will the Forster expander ball fit my bushing/shoulder bump die?

I have sent an email to Forster, but I don't know how quick they are and figured I'd ask here too.

Lastly, I will be sending my 6.5x47 build off to the gunsmith shortly, and this issue has given me pause. I am planning to go with a tight, no turn neck of 0.293". I already have a Redding bushing die, but this one has a expander. Will this and outside neck turning be enough to prevent donuts in that brass? My 6BR bushing die doesn't have an expander currently, could that have contributed to the donut formation? I checked my .308, and no donuts even with that neck die having no expander either. But it doesn't have a tight neck.

Thoughts?
 
Last edited:
THE DREADED DONUT. I HAVE HAD THIS HAPPEN WITH A 6.5-284 AFTER MANY FIRINGS. I have a mini lathe that works for this sort of problem. If you are tackling this with hand tools, you need the inside cutter. Without the right tools you could chuck the brass and start over. For the money you have invested in your rig new brass may be the way to go.
Enjoy
 
I'm gonna go with the K&M expander from Mystik. I could get the inside neck reamer pilot, but using that on the handheld turner would probably cause concentricity issues and it is cheaper to get the expander and mandrels then a new turner.

b72471 said:
THE DREADED DONUT. I HAVE HAD THIS HAPPEN WITH A 6.5-284 AFTER MANY FIRINGS.
Click to expand...

If you don't mind me asking, but what neck do you have in your chamber, and what dies do you resize with?

Tossing the brass seems excessive, I still get 1/2moa out of them.

I plan to build a .284 later this year, and I hear donuts are very common when necking up 6.5x284 brass, so I need to know who to deal with and prevent this issue.
 
Donuts are unlikely to be caused by a bushing die unless you've over-annealed your brass. When brass is healthy, they are the result of brass flowing forward from the shoulder area due to pressure. They happen, I've even had them in 308 Win.

http://www.canadiangunnutz.com/forum/showthread.php/330018-Donuts-vs-no-donuts-Pressure-Trace-data

If you try to push them to the outside, you will likely end up with a thin ring just above where the donut was after you turn the neck because there will still be a crease even after you try to push them out.

What I did was to run the expander into the neck having it stop just before the donut. Then I used an inside reamer to get it. Then I polished the area with 0000 steel wool on an old bore brush. After that I just adjusted the bushing so that it didn't size the last 0.100" of the neck. The brass may have still been thicker where the donut was, but the bullet cleared it and it didn't interfere with the bullet because that part wasn't being sized.
 
I would go with a no turn neck unless you are competing internaitonally,

brass seems to need 2 thou clearance on both side of the neck so a total of 4 thou

measure your bullets in the no turn neck brass and get some measurements and then decide,

you will not se much difference in accuracy unless off the bench with a 1200 neo and a flat 3 inch wide forend

and yes I shoot benchrest

Jefferson
 
Dropping the bullet in and having it stopped by the donut gives me an ogive length of 1.713". I seat them in loaded rounds at 1.788, and have 5x firings and no annealing on the brass.

kombayotch said:
If you try to push them to the outside, you will likely end up with a thin ring just above where the donut was after you turn the neck because there will still be a crease even after you try to push them out.

What I did was to run the expander into the neck having it stop just before the donut. Then I used an inside reamer to get it. Then I polished the area with 0000 steel wool on an old bore brush. After that I just adjusted the bushing so that it didn't size the last 0.100" of the neck. The brass may have still been thicker where the donut was, but the bullet cleared it and it didn't interfere with the bullet because that part wasn't being sized.
Click to expand...

I'll try pushing them to the outside with just a few cases, as a test to see how it works. I assume the partial neck sizing doesn't cause chambering issues?

Why would it create a thin ring above where the donut was? I can't quite visualize how that would form. I'll shoot the ones I expand, and then measure them again to see what happened.

If I end up having to get an inside reamer, so be it.

Jefferson said:
I would go with a no turn neck unless you are competing internationally,

brass seems to need 2 thou clearance on both side of the neck so a total of 4 thou

measure your bullets in the no turn neck brass and get some measurements and then decide,
Click to expand...

I've measured my 6.5 brass, going with a 0.289 bushing giving 2 thou tension and a 0.293 neck.
 
Alpheus said:
Why would it create a thin ring above where the donut was? I can't quite visualize how that would form.
Click to expand...

Understand that you're not dealing with play dough, you're dealing with metal that has memory and spring back. Have you ever bent a piece of sheet metal and then tried to bend it back flat? You never get rid of the crease. Similar when you bent a coat hanger and give it a sharp corner, and then try to bend it back straight and get the kink out? You never really get it out completely.

The thick material in the shoulder gets pushed forward from some very high pressure. It's also pushed to the inside by the same high pressure. Where the donut starts, where the material transitions from normal neck material to the donut, it isn't gradual. It's a step. It has an inside "corner" to it just like the inside corner of the bent sheet metal and the bent hanger. When the mandrel goes down into the neck and hits the donut, it will push it out. But that inside "corner" of the step will also get pushed out. The crease will still be there just as the crease in the sheet metal and the kink in the hanger are still there after you try to straighten them. The mandrel will not push them out perfectly flat. And then when you turn the outside of the neck, you will get a ring where that crease is. Here are some exaggerated drawings:





 
Ah, I get it now. Nice artwork. :p

Use of the expander mandrel and outside turning can't remove donuts, but can prevent them forming, correct?

Looks like I may be needing a inside reamer after all....
 
It does remove the donut, it just leaves a ring that adds a weak point to the neck. I imagine over time that ring would grow in depth and would eventually separate the same way it does when you get head separation. A band of brass around the bullet would likely cause a large pressure spike. I ditched the brass I did this to...

The idea is to turn into the shoulder so that the material is the same thickness as the neck. That way when it flows forward into the neck, no donut forms.
 
You must log in or register to reply here.
Back
Top Bottom