The barrel diagnostic is a complete inspection.
First we visually inspect the bore, chamber and crown with a top quality bore scope. We then measure the bore diameter and the groove diameter to see that everything falls with in acceptable parameters. Next we cast a short Cerro-safe slug in the barrel and slide it thru the barrel. If there are any tight or loose spots they will be detected here. We next pour a long Cerro-safe slug and slide it thru the barrel. This will show problems a short slug will not, such as consistency of barrel twist or changes in the land/groove width . Last we pour a chamber cast this gives us an exact picture of your chamber. It shows how well the chamber was finished at the factory, the neck diameter and a great deal of information about the most critical part of your rifle, the throat. We measure its diameter, length, lead angle, concentricity and wear.
All of this information gives us a clear picture regarding the rifles overall accuracy capabilities. If things are not right with the barrel then all of the other work is just wasted time and money.