The bore is centered with the barrel and the lug is slightly taller as the firing pin strikes the rim at the 6 o'clock position. As far as the explanation of the gap goes, Most people know there is a slight gap between the barrel and frame, on the top where the barrel rest in the frame, with the barrel horizontal that is. With the rimfire barrel in place the gap measures 25 to 30 thous. on each side, slightly more that with a center fire barrel installed. The gap isn't really visible unless viewed from the top. I love this barrel, it shoots great. Don't know why T/C didn't do this in the first place, guess it would have made too much sense.
Steve E.........