Here is a simple and EXACT way to measure.
1) You need the diameter of your action. I'll save you some time...if it is rem 700 or clone, it is 1.35". Anyway...figure 1/2 that (radius) and write it down. (.68")
2) You need to find the diameter of your scope TUBE (not the objective or occular ends). I'll save you some more time.... a 1" tube is obviously 1", a 30MM tube is 1.18". You need to find 1/2 of that (again..radius) lets use the 30mm...1.18 divide by 2 = .59". Write that number down.
3) measure your ring/bases from the BOTTOM of the ring where the scope sits to the bottom of the base where it contacts the action serface. lets say that this is .75".
Now, simply add them up....... .68 + .59 + .75 = 2.02".
Now, FORGET about the tapered ring bases....it does not matter which base you measure unless you are ULTRA ANAL....(like me
) Then you simply measure BOTH the front and rear ring/base...add them together, and divide by two and add that number to the action radius and and the scope tube radius. But, I'll save you even some more time just pick one and use that number, because we are talking fractions of an inch at 1000 yards.