Originally Posted by J E Custom
I would use the 300 WSM brass if I could not get the 7 WSM brass in the make I wanted.
You could size down the 300 brass and then turn the necks to true them and still have nice
thick necks that are uniformed.
Even the 325 WSM could be used but no matter which one you use you will have to fire
form the brass for the 7 WSM.
J E CUSTOM
I don't believe you can neck the others up/down to 7mmWSM due to the shoulder being further forward.
You could neck down from 300WSM brass and leave an auxillary shoulder to headspace off, but that alone can cause problems.
You would have to use a fireforming load, shotgun powder, cream 'o' wheat, and something to plug the case mouth like pumpkin or potato. This may eliminate the donut, but it may not also!
I think it's too much trouble bothering with, IMHO.