Greetings, What is the proper or most common method of measuring this distance? Where should the measurement be taken? And, does a tapered base influence the equation? Thanks for your input. Holmes

measure the obj.bell diameter(while scope is mounded)+diameter of barrel directly beneath of the obj. bell and divide by 2, then add the distanse between the barrel and bell. Atleast thats how i do it..

I measure the distance between the bolt and the tube itself then add half the diameter of each of them to this, close enough for me so far. I'm sure there are other ways to be more accurate but I'm not sure which is more precise.