Removal of "donut" from necked-up brass.

[arizonajake]

What is the most efficient method of removing the "donut" from .243 Lapua brass necked-up to .260 ?

I use both Winchester and Lapua .243 brass to make .260 Rem cases for silhouette shooting and only the Lapua brass forms the dreaded "donut".

Any help will be greatly appreciated. Thanks in advance.

 

[fdiazverde]

go to K & M & get one of this Carbide 4 Flute Neck Turning Pilot. frank

 

[Preacher]

Necking a case up .021 usually don't form a doughnut at the neck shoulder junction...
Your bullet shouldn't be below that spot anyways.... 'O(
K&M's carbide mandrel has doughtnut cutters on the shaft that will kinda remove them but a sized reamer would be a better bet if you could find one that cut exactly the size of the neck. Forster sells sized neck reamers.

 

[louielouie]

I've played with necking down 7-08 brass from Winchester & Remington to avoid the donut - now I'm wondering about the Lapua .308 "Palma" brass that uses a small rifle primer:
1. The Palma team claims better consistency
2. I've read a few places that SR primers are typically more consistent (maybe why #1 is claimed)
3. I'm having a hard time finding BR-2's but BR-4's seem to be every where.

Using some of my turned 308 brass - necking down in two steps to 264 - I can see that the 308 neck moves about 1/16 into the 260 shoulder so the chance of a donut seems small.

 

[1000yardstare]

ArizonaJake, I am with you on the dreaded donut and am also watching answers in this thread.

I am in the process of re-forming Win .243 brass to 6mm Super LR. This is just a matter of pushing the top of the shoulder down to form a 30 degree shoulder from the original factory 20 degree. Am using a 6XC F/L die to push the shoulder down. The die is too short to fully size the whole case but all I want to do is move the shoulder.

This process creates a longer neck with the top of the original shoulder now forming the bottom of the neck. I was amazed at the donut that was formed by moving the thicker shoulder brass into the neck. You can eyeball it from the outside.

I ran a 6mm expander mandrel down the neck to iron out the donut but now I have to consider some portion of the donut to still be on the inside.

Reading various sources on case prep and neck turning, I am going to try the method of skim turning the neck and biting slightly into the shoulder of the case with the cutter. This is supposed to create a void on the outside of the case where the donut brass will be forced into upon first firing.

 

[ronemus]

If you use an expander (mandrel or button) it will move the donut from the inside to the outside of the neck. That allows you to easily remove it by neck turning, which is a good idea anyway when you're reforming a case since brass doesn't generally expand/compress uniformly. New cases are never exactly uniform and tend to get worse when worked by reforming.

 

[DrJeckyl]

When I neck up 243 Lapua, I just touch up the outside of the neck up to and including the neck-shoulder junction..just a small amount to give the brass somewhere to go when first fired. This way it goes out instead of in...have yet to get a donut this way.

New on bottom, once-fired on top.

 

[Bob3700]

You can also check out any tool (Machinist) supply catalog and they usually have straight flute chucking reamers in 1/2 thou increments.

It is pretty easy to just run the reamer down the inside of the neck and remove any excess brass. MCS or KBC can supply them .2425 and .2430.

That is what I am using on my 243SLR with WW and R-P brass.

Bob

 

[arizonajake]

Thank you all very much for the information provided. I had not turned the necks all the way past the neck/shoulder joint on the cases. I will run the neck turner about 0.010" into the shoulder and see what happens.

Regards,