very important, i prefere to find the specs on my mounts and scope rings, you can also measure from the bottom of your barrel to the top of your scope at the bell subtract the radius of each and there you have your scope hieght. it's usually 1.5-1.8 on a bolt gun
Ive heard of another way. Take you caliper and get the width of bolt, width of scope housing and distance between the two. Take the distance between the two plus half the bolt plus half the scope and there u have it.
Well im not sure how accurate but what I did was pull my bolt back till even with the end of scope measure frome center of bolt to top of scope with calipers. Subtract half the radius of the scope and there ya have it..... Get ya within a couple thou.....basically what timmy said