The Lee Collet-Style Crimp Die sizes only the neck to preserve the perfect fit of fire forming. A collet squeezes the case neck against a preicion mandrel for a perfect bullet fit with minimum run-out. Besides being able to load the most accurate ammunition possible, this die is also the easiest and most convenient to use. It offers maximum accuracy, yet is less demanding is kept to a minimum and the need to lubricate is eliminated. Cases last about 10 times longer in this process. Only reload cases that have been fired in your firearm. Not recommended for autoloaders, slide, or lever action guns.