Here is a simple way.
1 Take a fired but unsized case.

2 Put a smalldent at the edge of the case neck so you can just seat a bullet by pushing it in with your fingers.

3 Barely start a bullet into the case.

4 Place this CASE/BULLET assembly into the chamber and close the bolt slowly.

5 Slowly open the bolt and remove the assembly.

6 Measure the overall length of the assembly.

7 Repeat steps 3 through 6 a few times until you get consistant readings.

8That is the length to the lands with that specific bullet.You need to do this withevery different bullet that you intend to load.

9 Simply subtract .015" or so and you have a good starting point for bullet seating.