It is called duplexing and it has been done since smokeless powder was developed. With the powders available today, there is absolutely no reason to duplex.
What Rangefinder is referencing by using fast powder at the flash hole and slow powder on top is an acceptable loading practice. Much of the published data for the older dangerous African game cartridges list an "igniter" charge.
Elmer Keith admitted late in life that some of the un-real velocities his wildcats achieved did it with duplex loads.
Last edited by reynolds357; August 17, 2013 at 04:38 PM.