How to prevent case head separation

[yobuck]

You don't appear unwilling to part with cash in order to get what your striving for. Which can certainly be a good thing.
I would recomend everybody carry a cleaning rod with bronze brushes, especially when hunting if at all possible.
But in a pinch, a green branch whittled to fit hard thru the case from the action end has been known to work.
As for the problem your having, it could be your overworking the brass, but changing your setup should tell you that.
Ive had head separation, but only on large capacity magnums with several firings on the brass. In fact I will no longer use
magnum brass fired more than 1 time for hunting, as I just wont chance a case failure. And I also try every round thru the gun.
We are talking about a standard factory rifle here, and id be curious as to just how much better it shoots using the dies
you've chosen, as opposed to just using standard say RCBS full length dies set up like the directions say to do it.
Just for kicks, separate some brass and either borrow or go on ebay and buy a set and find out if your problem goes away.
Annealing, and neck tension are unrelated as to the issue of head separation in my opinion.
You could also just get or borrow a sizing die and use the seater you have

[Idaho]

yobuck, I appreciate your thoughts. I have 100 new Lapua cases that I had prepped and primed. Part of the preparation was for me to run them through the case neck sizing die to get consistent neck tension. (I now know that was waaaayy too much) Tonight I dug out the size button for the decaping rod and lubed the inside of the necks and ran then all past that button in the die. Then I loaded up 10 cases and am amazed at how much easier the bullets seated. (one of the new collars that I ordered for the neck sizing die will duplicate this effort)

Now, I can't wait to get to the range to see if it makes any appreciable difference in MV spread and accuracy. I like puzzles. Mostly, I like chasing the secret to extreme accuracy. It still elludes me but I'm getting closer and having a blast along the way.

As to annealing the cases, I agree, I don't think it will help appreciably in my case. (no pun intended) Anyway, the new Lapua brass is clearly annealed and ready to go.