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The "Donut"

The second consideration is the formation of a "donut". This is a ring of thicker brass inside the neck of the newly formed case. The donut appears when the neck-shoulder junction of the newly formed case ends up closer to the base than the parent cartridge. This donut must be removed or dangerous pressures will result due to the lack of clearance for the case neck to release the bullet. Again, we recommend a minimum clearance of 0.003".

Neck Thinning

There are two common methods used to reduce the neck wall thickness of cases and remove donuts from their necks. The simplest is neck reaming. Reaming can be performed on a case trimmer or in a special reaming die. The die method is preferred, as the reamer tends to follow the off-center hole in the case neck when reaming on a trimmer.

The preferred method of thinning case necks is to use an outside neck turning tool to remove brass from the outside of the case neck. If the neck turning operation is performed one or two calibers larger than the final desired caliber and a size button is pulled through the neck, it will also remove the donut from the case neck. Neck turning produces a more uniform and concentric case neck than the previously mentioned method of reducing neck wall thickness, reaming.

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Originally posted by Harley:


I must ask what rifle and scope is in your sign off line????

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