As Partagas points out, the powders in Hornady's Light Magnum loads and RCM cartriges produce higher velocities than those currently available to handloaders. At some point in time they may become available to us.
However, the currently published RL17 data is nothing to get excited about. The results some shooters are getting with RL17 exceed the velocities produced by the labs. Why? I do not have the answer.
Perhaps as more shooters work with the powder and a greater body of data is produced we will find that the currently published lab results were an anomaly on the slow side.
