Thanks for stating the obvious. Again, it's just a comparator, none of which I'm aware, can take the place of measuring to the lands in your chamber. But it will fit your bullet very well and very much like your actual chamber...allowing accurate measurement of the bullet or loaded round....which is what was stated in the op.
Now, depending on how you make yours, it can be used to establish distance to the lands(new barrel), neck clearance, and shoulder bump. It can be used to sort bullets bto as well as loaded ammo, both bto and base to datum. All in one little tool. But no, it won't take the place of chambering a long seated bullet in your worn barrel.