If hand loading and wanting to confirm lands measurement, one method I'd read about and now use is to start with a few neck sized cartridge brass previously fired from the subject gun. Seat the desired bullet long into the otherwise empty (dummy) brass and chamber it. The bullet will probably be driven back into the brass by this action and stick in the lands. Tap the dummy out with a cleaning rod and place it in your press with a seating die. Adjust the die to drive the bullet back just a few thousandths. Then using a new similar brass, install a new bullet slightly deeper and chamber it. Remove as before and inspect. Adjust your seating die again and keep doing this until you get no engraving on the bullet. Some use the same bullet over and over and clean/paint the bullet each time. I like to see/measure the progression so i use several.