I think the Larry Willis dies are a bit of a scam. He promotes them for preventing case head separation in belted magnums. Case head separation is caused by full length resizing a case over and over to give excessive headspace each time, and the resulting case stretching. It is aggravated by having an excessively long chamber. That is not fixed with a Larry Willis die. It is fixed by not oversizing your brass. Bump the shoulder 0.001" and no more.
His collet dies are "NOT" a scam, if you adjust the die for minimum shoulder bump the die stops resizing further up from the belt. When you resize the belted case to headspace on its shoulder you "MAY" need the collet die to reduce the case diameter just above the belt.
If you would simply Google the subject you would find many shooters saying it solved their belted case problems. (instead of guessing)
The problem is some dies and brands of brass are not reduced in diameter above the belt and rub and bind when chambered.
This is no different than having to use a small base die with a standard non-belted case and reducing the base diameter to SAAMI minimum.
Dies are made to plus and minus tolerances and if the die is on the plus side (a fat diameter) the base of the case may not be reduced in diameter enough to fit the chamber properly.
Making the base of the case smaller in diameter is not a scam, it is a fact of life with some chambers and dies.





















































