300 WSM Doughnuts?

[SHall]

I have been playing around with a 300 WSM, No Turn (.343nk) for 1000 yard benchrest this year. I had a fellow shooter tell me I would start getting a doughnut forming after a few firings of my Norma brass. Has any of you experienced this? I am only bumping the shoulder back minimally, 1 thou or so. Samuel Hall

 

[dkhunt14]

I am not sure what causes this. My buddy gets them from time to time and I don't. The rifles are the same Reamer. I even bump mine harder. Both are Norma brass and same powder, and bullets. Almost has to be in the dies or neck turning. But both of ours are .338 neck amd need turned. Matt

 

[SHall]

Matt, what you said makes perfect sense! That is what I was thinking also. Thanks! Samuel Hall

 

[mikegaiz]

I have gotten them, but after about 10 loads. I use the K&M neck turning carbide mandible to remove.

 

[jfseaman]

Though I don't have them on my 300 WSM, I have gotten them on other chamberings.

I use a .002 over size expander mandrel and neck turn just to remove the doughnut, just barley touching the neck at the mouth.

 

[Richard Coody]

What is happening is thicker shoulder brass slowly migrates into the case neck. That is why when you neck turn you want to cut slightly into the shoulder. Thin that shoulder brass. You can sort of judge how fast it is happening by how much your neck is growing and how often you trim. Hot loads will speed it up.

I like the push the donut to the outside and neck turn it off. This is a procedure with lots of strong opinions. Whatever works for you.