I was playing around earlier and thought about it (as i loaned my 308 dies out) so ran one in and then compared it to fired unsized cases, remarkably similar. Can it be done safely?

If your just neck sizing I don't see why not as long as you can size the whole neck.

I beleive it will work. THe 308 is about .1" shorter than the 300wsm in the whole case and in the shoulder length. That means that you will be resizing a little less neck with that die, but it should still work for sizing the 308. I used to use a 308 die to neck size the 30-06 (same principle).