The Lock-N-Load O.A.L. Gauge is universally acclaimed as the most accurate, easy-to-use and reliable method of regulating seating depth and the resulting "jump" to the rifling. This straight OAL gauge works for all bolt-action and single-shot firearms or any firearm with straight-line access to the chamber. NOTE: To use the Lock-N-Load OAL straight gauge, you will need a modified case to fit your firearm's chamber (not included).