My first guess would be that the expander ball stem needs adjusted slightly, so that it is passing down through the neck at the right moment, when the neck is engaged into the throat of the resizing die.
The expander ball stem could also require a good polishing.
If you remove the stem and Chuck it in a drill, a good rouphing with 320gr. sand paper followed by a thorough polish with 0000 steel wool will remove a thou or few and tighten the sizing of the neck.
A quick mic of before and after diameter of the resizing ball and the brass neck inner will probably get it doing what you need.
Size three pieces of brass before as a control.
Then check progress after the polish.
If necessary the process can be repeated.
Just use steel wool only for second or third polishing.
I polish all my stems to smooth the process up and have had some that were pretty rough.
Hope this helps.
I do not load 300 wsm and have not heard of this problem from anyone else that does. But have had similar trouble with some REM. 260 years ago.