Collet Die Explanation

The Collet neck sizing die is superior to the competition's neck sizing die design because it squeezes the neck against a mandrel.  This results in very uniform case mouth inner diameter, regardless of case wall thickness. 

With bushing-type neck sizing dies, one has to select (and usually purchase) the appropriate bushing to get the desired case mouth inner diameter.  Uniform case mouth inner diameter gives uniform bullet pull, and as you know, uniformity is what accurate ammunition is all about. 

The Collet die set also includes what we call the "dead length" bullet seating die.  This die is set up like a full length sizing die, in that one adjusts the die down so that the shell holder presses against the bottom of the die when the ram is at the top of its stroke.  This pressure removes any clearance between the shell holder and ram, lever linkage, die threads and press frame, etc.  and results in a more uniform bullet seating depth.  Note that there is no provision for crimping in this die.