Does it appear to hit a parallel section? If so, and that's approx. .410", that may be the barrel ID. Depends on how long the taper leading into the cinal choke diameter is. I have a similar gauge and measured my Browning M42 by using a telescoping gauge to determine the bore I.D.(.407" in my gun). The choke measures .396". My choke is therefore .013". The barrel is marked "Full". Skeet targets believe it is full, when I center one. I have a Skeets bore mike set but it only goes small enough for a 28.
