A while back he told me what the minimum dimensions of a 12 Gauge barrel were to fire one of his loads (and load information too. Used - I think - Reloader 17). I can't remember where I tucked that information away right now. Probably be faster for you to ask himdirectly. With that load he was approaching the .458 Winchester Magnum for Muzzle Energy.
I don't think I'd want to shoot that from a NEF. Tear your shoulder off.