This problem has been with us for a very long time . "season cracking " is technically " stress-corrosion -cracking" .Lightning causes ammonia compounds to form and corrode the brass [other things can add to that] .The stress of course is the forcing the bullet into the case .The wet season is when the lightning is present. The solution , known over 100 years is to anneal the necks. Just ask one of us metallurgists ! 