Win 338 brass is decent stuff.
I've made 338's from 7 rem brass and it can be done but win 7rem brass will have very thin necks. Rem 7rem brass is better for necking up. You will need to go to 30 cal first unless you have a tapered expander.
I've pushed 300 win shoulders back for both 7rem and 338 win brass and they wrinkled a bit but shot fine. Not quite as bad as fireforming 7rems into 7stw's I suppose...
Don't try that one at home boys and girls.