RE: Lee collet neck sizer?
Well, could be a number of things. A chamber that has some wobble can cause this. In other words, your FL smaller brass fits fine, you then fire and fireform to the chamber and now hard. I can't say it should act like this from one firing. It takes me 3 or so firings for hard chambering. And this is 3 calibers or so and the lee.
I wouldn't get too worried if it shoots well, you just might have to FL everything. Now if it shoots bad, thats another issue.