honestly, the only idea that I can think of is that the collet sleeve is over stressed when tightened down. In otherwords the neck diameter is too big. The best way to stop this is to make the tapered I.D. of the body of the die a couple thousandths smaller, and also make the neck diameter about three thousandths smaller. The actual sleeve is a copy of the Hardingh Brothers design, and used all the time in machine shops. Very accurate, but the actual working range is fairly minimal. So if my chambers were two or three thousandths bigger all the way around; I think it would work well.
gary