Hornady Lock-N-Load modified cases are designed to work with Lock-N-Load Precision gauges. A special fine thread is used to attach them to the gauges ensuring that they remain perfectly square for precise alignment in the chamber of your firearm. Second the neck of the case is made perfectly round and opened slightly to allow a standard diameter bullet to slip into the case mouth effortlessly but concentrically to ensure the most precise results possible. Hornady offers Interchangeable Modified Cases in all common sizes. These specially prepared Modified Cases are threaded at the case-head and have a .002" oversized neck to accept the same bullets you intend to load.