castnblast,
Let's get the nomenclature correct. The head is that portion of the case that contains the primer pocket and chambers toward the rear of the rifle. The part you may need to anneal is the neck. It is normal for the annealing to include some of the shoulder, and I have annealed down past the shoulder about 1/8 -1/4 inch and I it did not cause a problem. If you anneal the other end of the case, the head, you may destroy the primer pocket and never get a primer to hold again. If the head is annealed the primers can actually fall out when you extract after firing, because the brass has lost it's springiness due to annealment. The area around the head of the case needs to stay hard. Don't anneal it.
But, yes, once the neck is hot, submerse it immediately. If you try to do too many at the same time, they can cool slowly and that will harden the necks and you could see neck splits. That's why reloaders that do this and don't have an automated process, do one or two at a time and just tip them into a waiting pan of water.
