The story that I heard...and my bad memory says it was from a pre- or post-performance commentary by either Wild Bill Moses in Phoenix or Bill Monroe in Memphis, was that the "cannonball" term was a reflection of a faster-than-normal train, and that Daddy Claxton was, as I recall, either an off-duty or a retired engineer from that train who was asked to fill in because of an absence of the regular driver and a need to make the run because of some time crunch - he was like the Michael Jordan of trains who was the last, best chance for the run to be on time. Again, as I remember it, there was some sort of accident to the train as he was cannonballing and he was killed trying to do his job. The reference was that they were taking his remains back home.