Once a barrel is running in the steady rest or headstock, insert the range rod into the bore and set the indicator to read on the surface of the indicator rod. The removable pilot indicator rod centers itself in the bore, effectively indicating off the inside of the bore for a perfect inline bore.
Rods have a removable pilot and are made of steel.
This Range rod is tapered so that when inserted into a non-chambered barrel blank, a small section of the rod will protrude from the bore. The rod will be aligned with the center of the bore due to the pilot and the rod's taper (near the end of the rod opposite the pilot). The rod can then be used as an index point to assure that the blank is centered in a lathe prior to any machining operations.
If using a pre-chambered barrel, a PTG Indicator Rod will work better, since the taper in that rod is much closer to the pilot (the rod will center in the throat area of the chamber and still protrude from the barrel at the breech.
Range Rod: new, unchambered barrel blank
Indicator Rod: barrel that has been chambered