You seem to have a sizing problem.
Sounds as if you may be stress hardening the necks due to resizing. If your die resizes the neck excessively the neck will stress harden and split when shot.
Splitting after only 3 shots is a bit unusual.
A couple of options are:
1) Anneal after every two shots. (A real pain)
2) Measure neck diameter after firing and after resizing. This would be a neck tension measurement. If it is excessive a better sizing die could be needed.
I don't know what is excessive or which bushing die is better.
I'm confident some one will chime in with the correct sizing info.
I have never had your problem with my 338 RUM. Mine last 5 or 6 shots due to primer pocket growth. I stoke it up pretty well.