First - the folks at Lee (with the exception of one call) have been pretty good to deal with, but so far, I've not made any progress with them on this front. They have flat out told me that they will not change the mandrel unless they hear from a lot more people. . . I told them that as more people adopted Lapua Brass, they would certainly hear.
Bottom line (after having sent the die back twice to Lee) is that the Lee Collet die not work with your Lapua 6.5 Creedmoor brass. This is for two reasons (one of which is much more significantly detrimental than the other, in my view):
1) The diameter of the decapping pin is greater than the diamter of the flash hole. As a result, the die will expand your flash hole. I know there's debate around the diamter of the flash hole, so please leave that for somewhere else. I'm just pointing out facts: One trip through the die, and your flash hole will forever be expanded.
2) The base (I'm using this term imprecisely) of the case is too thick to allow the case enough vertical movement for the case neck to get "inbetween" the petals to be sized. If you try to apply "just a bit more pressure" (never cam over with this die!) you'll end up "bottoming out" the mandrel on the case web, and you'll get non-concentric sizing at the top. Even with the 1/8th turn approach, I was getting almost 10 thou runout measured using my concentricity gauge.
What's the solution? Well, one must either a) abandon Lapua Brass, or b) remove the decapping pin from the mandrel AND THEN grind off additional material from the bottom of the mandrel to allow concentric resizing.
It's no bueno from my point of view, so I'm hoping that more and more Lapua Brass shooters will let Lee know that this isn't ideal.
Please, please refrain from telling me about additional ways to neck-size brass. I am aware of them, and have more than likely tried all of them as well. There are some real benefits to the Lee die. I suggest you all look into it if you're not using it already.