I recently purchased the Hornady Bullet Comparator, and it is probably one of the simplest and most accurate way to measure your seating depth consistently, as it measures off the ogive of the bullet (not the tip, as there can be "semi-large" differences between the overall length of each individual bullet) therefore, the length measured by the Comparator is shorter than COAL (ie. 2.130" vs. 1.792" in a .222 Rem). You would have to measure the COAL without the tool first tho to make sure they are in spec with length (not really that important unless you are using them in a magazine or hinged floorplate, etc.). If you are using the rifle as a single shot, the Comparator works beautifully with the Hornady O.A.L. Guage, but usually the COAL is over SAAMI specs when done this way.
Red Mist. It's an addiction!