I'm looking at getting some target turrets made. I need to measure from center of Bore to Center of scope ObJ. What is the most accurate way, to get the center measuremant of the Bore. Put a rod in the bore, Measure to the center of the cleaning rod??? OR is this measurment necessary. I'm sure if you do not get a real accurate measurment, the turrets will be way off at 500 plus yards. What about the cheap $99 chrono's, are they accurate enough to be trustworthy. Anyone reccommend some good turrets. Kenton IND is the ones I'm looking at. Thanks All.