Jon Speed's book Original Oberndorf Sporting Rifles pages 340,341 ,342 lists these shooters using the 404
Mickey Norton
Pete Pearson
John (Pondoro ) Taylor
Bruce Kinlock
Jos'e Simoes
Alfred Pease
Denis Lyell
Edison Marshall

If you get a copy of Legends of the African frontier .It gives a pretty good history of most of these guys.
hope this helps