You are simply not getting the necks sized down properly to to hold the bullets. Whether it because the case necks are to thin or the hole in your sizer is to larger it`s all the same out come. Don`t throw the Win. brass away, just put it back untill you get a good single stage press and some good dies. AND when you get a single stage press get anything but a Lee. I started loading my own in 1965 and have had alot of Lee junk over the years, and sooner or later it all let me down, no matter how much I liked it when I first got it.