make sure the case is tight on the tool,put the bullet in the mod case deep enough that its not touch the lands,insert the case/tool into the chamber with the thumb screw tight went the case is all the way seated loosen the thumb screw and slowly push the dowel in until you feel it touch the lands,stop and tighten the thumb screw,pull the case/tool out push the bullet out with a cleaning rod drop it back into the mod case and check you measurement(the riffle does not need to be facing barrel down because the bullet will stick in the lands)the two most important things are to make sure you push the bullet into the lands using the same amount of pressure and when measuring make sure you also use the same amount of pressure on your calipers. take 5 to 10 reading(10 being better)and go with the most consistent measurement.