What causes doughnuts

[Austin]

What causes doughnuts.I never new why.

 

[techshooter]

Brass from the thicker case wall areas in the shoulder area migrate into the neck area due to cold flow from the pressures in the chamber at each firing. It is exacerbated when necking up a caliber or two, such as making 260 brass from .243 brass. Cases with shallower shoulders tend to have more migration, and steeper shouldered cases,like Ackley Improved 40 degree cases) typically have less.

I just recently had a donut issues with 260 brass from 243 Lapua. Look here for a shot description and a closeup picture of a donut:

http://www.the-long-family.com/260AI.htm

Hope that this helps!

Cheers,

 

[Forum Boss]

Like Chris, I had bad doughnut issues making .260 brass from .234 Lapua and .243 Norma. The situation was pretty extreme because I was shooting the brass in a factory chamber with quite a bit of taper in the neck. This meant excess space right at the neck-shoulder junction. Within three firings the brass thickened so much at that point I couldn't seat a bullet far enough in the case to close the bolt. The solution involved inside reaming and outside turning. Other guys are just shooting the Rem 260 brass to avoid the issue. That may be the way to go for applications not as demanding as benchrest.

Before people buy a standard .260, however, I tell them to take a hard look at the ballistics of a 6BR or Dasher shooting 105s. I concluded the 6BR made more sense for paper punchers.

 

[Austin]

Thanks for that.Thats all till the next question.:thumb:

 

[Varminator]

I've found doughnuts in new brass using the K & M inside tool. I now size after fireforming then expand with the expandiron and kiss the outside and remove the doughnut. No more problems for the life of the brass, generally.
MM