Big Country, I misspoke. You vary (reduce, usually) the I.D. of the case NECK ONLY. You do this by using a smaller expander button. As an example: I once tried this with a .450 Alaskan M71 Win. I used .452 expander plug from a .45 ACP die to size the mouth afer running it through the .450 AK FL die, from which I had removed the expander stem. I belled the mouth of the case slightly with the .452 pistol die expander, so the bullet could be started without damade to the case mouth. Using Speer 400 grain bullets powered by 64 grains of 4064, I fired four rounds leaving two other rounds in the magazine while shooting. There was absolutely NO movement of the bullets into or out of the case neck, despite having had NO CRIMP. The powder charge was big enough to keep the bullets out of the case, but the bullets didn' t move at all during this test.

Actually, a lot of dies that are used for crimping will cause the case neck to EXPAND AWAY from the bullet shank when the crimp is applied. However, I think (not sure) that the Lee" Factory Crimp" dies are an exception to this.