Are you sure about the 6 1/2 inches? I have two IP's with what I believe are the original barrels. One with a serial number in the 3.2 mil range has an Underwood 11-42 barrel with two proofs; one 4 5/8 down and one 6 5/8 down. The second IP in the 1.7 mil range has an Underwood 3-43 barrel with one prooof which is 6 5/8 down.