If you try it without the false shoulder, it could cause case head separation when the case stretches to fill the chamber....or shortly there after...maybe one or two loads later. The old way was to jam the bullet hard into the lands. But the case is still driven forward when the firing pin hits the primer that way. It can still stretch the brass as it expands to take up the free space.
With a false shoulder the firing pin will not drive the case forward hardly any if at all.
The 300WSM run into the die of the 7mmWSM should be ready to load and shoot......the 270WSM brass will need to be necked up to 300WSM then back down to 7mm to create the shoulder.
Also, when necking to 7MM from 300, neck it down just enough to be able to close the bolt.....it should be a tight fit so that the false shoulder is pushed FIRMLY into place. That will give the best results.
Keep an eye on neck thickness and over all case length.........should be fine but I always measure just to be safe.
Hope this helps........there was an article SOMEWHERE on the 6mmBR site.......but I can't find it anymore.
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