Hornady Lock-N-Load Series Modified Cases are specially modified to work with Lock-N-Load Precision gauges. To ensure that they remain perfectly square for precise alignment in the chamber of your firearm, a special fine thread is used to attach them to the gauges. In addition, the neck of the case is made perfectly round and then opened slightly to allow a standard diameter bullet to slip into the case mouth effortlessly, but concentrically, to ensure the most precise results possible. Specially modified to work with Lock-N-Load Precision gauges Perfectly round case neck, slightly opened Engineered for precise alignment