Lyman's MSR Die Sets are engineered specifically for MSR ammo and are a must for anyone reloading for a modern sporting rifle. The sets include a Small Base Sizing Die designed for semi-auto use which will size cases to a slightly smaller diameter to ensure smooth chambering. Each die set comes with a separate Seating Die and Taper Crimp Die. The Taper Crimp Die is designed to give you added bullet grip for functioning through semi-auto actions. Straight walled cases come with Lyman's famous "M" Neck Expanding Die. Lyman's MSR Die Set also includes an Ammo Checker gauge, machined to minimum chamber specs. If it fits, it will chamber. These dies have a black oxide finish and are packed in a foam lined storage case. This item is for 450 Bushmaster.