The Lock-N-Load O.A.L. Gauge is an easy-to-use and reliable method of regulating seating depth and the resulting "jump" to the rifling. This curved OAL gauge works for all autoloader, lever or pump action rifles; all bolt action and single shot firearms. It is not compatible with Adapter "D" or short-bodied cases. NOTE: To use the Lock-N-Load OAL straight gauge, you will need a modified case to fit your firearm's chamber (not included).