There is a simple way to set the COL to lands distance.
Put a bullet in an empty case, leave it long , then chamber it, measure, chamber again until the COL is the same after several cycles.
If it fits the magazine, great. Now using your seater stem, which are generally 28 tpi (quarter inch fine) or 0.357" per revolution, screw it down 1/4 to 1/2 a turn and your done.
The bullet in the dummy round is now your reference bullet, as mentioned previously the bullets vary in length, what you are doing in the above is finding base to ogive length.
Keep the dummy round in the box of bullets as you will change the COL to chase the lands and/or tweak your powder charge.
I do this every time I clean the barrel, 150-200 rounds.