Why do you need to messure the shoulder bump? If your rifle have fired the cases you just might need to necksize them or to partial size them. If you use them in several different rifles just full lenght size them so you dont have problems in your AR. What are CBTO? If you want to messure the coal take an fired case pressure the neck with a tool or against your bench so it can hold a bullet, chamber it , push it out with a cleaning rod and messure the lenght.