The easiest and simplest way to determine where the lands are for any particular bullet is to grab a once fired case that has been neck sized only, and cut 2 slots in the neck opposite each other with a dremel or hacksaw. (You will need to neck size this doctored brass each time before you use it.)
Seat a bullet out long and carefully hand feed it into the chamber and close the bolt on it.
I found my best and most accurate reading by opening and closing the bolt several times without removing the bolt, then carefully extract the cartridge, being careful not to hang up the bullet on the way out, (if you have a plunger type ejector, you will need to keep finger pressure on the side of the cartridge while it clears the ejection port so that it doesn't drag on the side of the action.) whatever the overall length is is the OAL to the lands for THAT bullet, this will change with each bullet style and weight.
I actually measure to the ogive on my rounds, but this will still work to some degree of accuracy with non lead tipped bullets.