The gun you're referring to must be the "JAM" gun. I know that Peter (the former head gunsmith) has talked about this gun. He helped John with some of it, as John was his assistant in the repair department for a while. JAM was, of course, John's initials. The CR prefix, if I recall the story correctly, was tucked under the grip/stock, such that only "JAM" could be seen as the serial number. I believe the lockwork, and possibly also the barrel and recoil system, were fitted by Peter after John cut the thing down to miniscule size.
Last I heard it was in the Gideon collection, which is currently being evaluated for an estate sale. It may be one of the guns rumored to have been sold previous to Bob's death; to help pay for medical costs. You might try asking Awedfellow at the Detonics Collectors forum on Yahoo. Perhaps he could add some more info.
Hope this helps, ...Deeton