Mmmm, donuts....

[Onewolf42]

My new 284 Win barrel (26", 1:8) was delivered from McGowen last week and I put the rifle together (Savage 110BA action, MDT/Oryx chassis) and shot my first 12 rounds with the rifle this weekend. My goal was to produce some fired brass that I could use to confirm that the barrel had been throated to set ELD-M 180s at 3.24" COL (+ 0.02" jump).

I noticed that 3 of the 12 fired rounds had noticeable 'donuts' that prevent the ELD-M 180s from being set at 3.240" without being 'in the donut'. They could be set at 3.265" however that will jam them slightly.

I originally made the 284 brass by neck sizing the Lapua 6.5-284 brass to 7mm. I have shot this brass (~100 pieces) 3-4 times each with A-Max 162 bullets (longest I could mag feed in the old short action).

Question: Why are some calibers more prone to donuts than others?

What are some good methods/processes for avoiding producing donuts (or dealing with them when they occur)? I have another 100 pieces of new/unmolested Lapua 6.5x284 brass that I need to resize for 284 Win so if there's a better process than simply neck sizing and shooting, I'm interested.

Thanks.

 

[ZiaHunter]

Donuts with necked up 6.5x284 brass is very common. One of my F Class rifles is a straight 284 and consistently have donuts even with turned necks. This is dealt with by a longer freebore which allows the bearing surface to sit above the donut when seated. You can use a inside neck reamer to remove the donut but in my experience it has created issues with neck tension.

 

[spife7980]

Yep, necking up moves the often thicker shoulder material out into to the larger diameter neck base and thus the donut of thicker material. Thast the crux of the donut. Even without necking up as brass migrates it can move enough to shows its ugly head.

Turn the necks with a 35° angled cutter and cut just into the shoulder a smidge to help thin that material shoulder material so its no longer standing proud of the rest of the neck once it migrates.


I would have wanted to make some of the brass first and then have the barrel cut to fit it like zia describes to avoid it all together.

 

[IHFarmer07]

Honestly, every cartridge has donuts. Some are worse than others but I’ve been told it depends on your reloading and sizing.....I have found most all have the issues.

I’ve tried reaming but I don’t have a good setup for that and you have to have just the right size to do want you want. Either you have it throated a bit more to get the base of the bullet above the donut or neck turn with the degree cutter as the degree of your shoulder or close to that degree, this is a MUST! Neck turning has eliminated it for me but you need to just touch the shoulder/neck junction to get the donut fully taken out.

 

[918v]

When you neck up, you make the neck thinner. When you size the case, brass flows forward. The shoulder material flows into the neck, making it thicker. When you size the neck, the thin material gets sized as well as the thick, forcing it to the inside and forming a step in the neck wall which people refer to as doughnuts.

Neck turning induces the same condition. You make the neck material thinner but the shoulder material maintains original thickness which eventually flows into the neck.

 

[918v]

If you use correct for caliber brass you’ll prolly never get doughnuts.

 

[Joel Danielson]

Lapua 284 brass coming in the spring!!

 

[crunchy]

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