The Short Action Customs Modular Headspace Comparator Straight Bullet Insert uses a 3.0 degree "lead angle" to contact your bullet's o-give in the exact same location as your barrel does, giving you the most accurate and useful measurements. This comparator utilizes a o-ring design, allowing you to quickly change bullet inserts on the fly as well. FeaturesManufactured from 17-4 StainlessNote: Modular Headspace Body sold separately (product 1025514594). Straight bullet inserts are for individuals loading magazine length or using small bullets that o-give sits very close to the case mouth of the cartridge.