gunboat57:  Krag barrels and receivers have an index mark.  It is viewable (when the barreled action is out of the stock) on the right side at about 3 O'clock.  You should see a fine line on the face of the receiver ring and this should match a fine line on the barrel.  Also, the flat upper surface of the Krag extractor serves as a good reference point to tell if sights are in 12 O'clock position.