A collet squeezes the case neck against a precision mandrel for a perfect fit with minimum run-out. No case lube is needed. Cases last ten times longer, so the savings on only 35 cases will pay for the dies. Maximum accuracy is usually achieved by seating the bullet out far enough to touch or almost touch the rifling. These dies size only the neck to preserve the perfect fit of fire forming. Only reload cases that have been fired in your gun. Mfg: Lee Precision