Thick necks can cause high chamber pressures and erratic shooting. Wilson neck reamers remove excess neck material to insure adequate clearance exists between the case neck and the chamber. Also, these reamers can be used when forming wildcats from a parent case. Reamers are used in the Wilson trimmer in place of the trimmer cutter. Standard reamers are sized for use on fired, unsized cases and measure .0025" - .003" larger than bullet diameter. Custom size reamers can be ground (allow 6-8 week delivery). Mfg: L.E. Wilson