Just to mention it, I have had the "bullet fall into the neck" problem. Way back when, I had been Partial Resizing cases for my 220 Swift, and thought maybe a NK sizer would be a good addition. So I bought one, sized a bunch of cases, primed them, put powder in one and went to seat a bullet. The bullet fell into the case. The sizers did not size to the same degree. I got new brass and that solved the problem. In my case (no pun intended), the old brass had thinned necks. But, the fact remains that the two sizers did not size necks to the same degree, and the problem could have been the expander ball.