I make 358 from 308 using the 358 sizing die. You're essentially doing the same thing. I happen have dies for 32 Spl. so I usually do the expansion in two steps but have done it in one step, no problem. As mentioned, use lube on the inside of the neck and just take it easy, it'll go fine.
Since the headstamp will read 30-06, you might want to consider marking the expanded cases so you don't try to shoot them in a 30-06 though. I don't own a 308 so that's not problem for me.
Dale
