"The problem arises when a full length sizing die is raised in an attempt to neck size only. The portion of the die that normally contacts the shoulder of the case no longer does so. If the body of the case is contacted and that portion of the case is reduced in diameter the squeezing of the case actually extends the length of the normal head space measurement. This is what creates the situation where the case will no longer allow the bolt to be closed and the case chambered."

Yes, Big Bob, I can see where that could happen, particularly in situationswhere a person's rifle chamber is big enough to allow a case to expand excessively, and upon sizing the "extra brass" has to have someplace to go when the case is squeezed back down. I stand corrected! Such an occurrance would certainly explain a lot of apparently strange happenings.....

I'm awfully old, but I hope I never get too old to learn something new!