The "dreaded donut"

[redleg1013]

Forgive me if this comes across as hijacking, as I didn't want to start another thread to cover the same question.

If, in standard cartridges (308, 30-06), a person wanted to neck turn, to improve case runout, would it necessarily mean that it would cause a donut?

 

[keithcandler]

It seems to happen more on necked up brass because you open the necks down into the shoulder but it can happen on necking down to. Like stated above turning into the necks helps and having enough freebore in the chamber to get out of the ring solves the problem. I have a turning mandrel on my K@M that has the cutter to cut out the ring on my 30-28 works pretty slick.

Brass flow from base to neck is normal. How much and when it becomes a problem is the question.

As Sherm mentioned, push a bullet in the case mouth after firing. If the base of the bullet goes past the shoulder neck junction, then that particular piece of brass is OK.

K&M makes a carbide mandrel that cuts the doughnuts out real quick.

Some time ago, I have 4 brands of new brass Rockwell tested, 100 cases each. There was a 6% variation over a particular brand of brass, and a 12% over all variation in all brands from softest to hardest. This explains why some primer pockets seem to give out sooner than others and why some pieces of Soft brass develop doughnuts.

When making wild cat cases, I always do an initial neck turn at the larger dia case, then part of that thinner section becomes part of the shoulder when fire forming.

40* Ackley shoulders seem to limit dramatically the formation of the doughnut, but this does not apply to the 30* shoulder angle.