500,

You might be able to get a fairly accurate answer on that from those single shot pistol forums. I think there is an active one on AR. A lot of these blokes have rifle calibres chambered in those things and I think they might have barrels in the 15 to 16 inch range. I think 375 Win Big Bore and 444 Marlin are common chamberings so velocity with those in the pistols would probably relate quite well to the 458 Lott as "rifle" velocities are similar with all three.

Mike