This die sizes only the neck to preserve the perfect fit of fire forming. A collet squeezes the case neck against a precision mandrel for a perfect bullet fit with minimum run-out. No case lube is needed. Cases last about 10 times longer. Only reload cases that have been fired in you firearm. Not recommended for autoloaders, slide or lever action guns. Notes: Collet neck sizer uses a collet to squeeze the case neck against a mandrel, creating a precisely aligned case neck while reducing runout.