Having done hundreds and hundreds of 30BR cases with the Lapua, there's only been a few neck splits during the expand up process. But stuff can happen. I've always found the Lapua factory stress relief to be fine for expanding to .30.
I just did these for a new barrel. Single pass over a tapered 6 to .30 expander, into a .327 neck non bushing full length die to straighten the necks and neck turn over a carbide mandrel. The neck/shoulder area gets a light stress relieving as the final step. At that point, they are ready to shoot (primer pocket and flash holes are also done). Load work can start at the first firing. The same process is used whether it's Lapua or Peterson 6BR brass. On Peterson
7BR brass, I don't stress relieve the necks as they are significantly more malleable (pre-expanding) than Lapua or Peterson 6BR.
Good shootin'

-Al