Proper hemping of a drone reed seat is just about patience and getting the hemp to conform to the exact shape of the reed seat. Take your time and add hemp where necessary. Notice that as it gets to the right thickness it takes on a shiny/darker look. This happens when the hemp is compressed and indicated that it's contacting the inside of the reed seat.
This post is written by Dr. John Holcombe.
One of the biggest fears some pipers have is that one of their drone reeds will suddenly come out of its reed seat and fall into the pipebag, leaving you with no ability to play. If this ever happens, trust me here, it will occur during one of your most important performances. But there is a way to totally eliminate the possibility of a drone reed becoming dislodged, and that is to “thread” the reed seat using a commonly found tool.
Don’t you just love the sound of a beautifully tuned bagpipe? The full harmonic sound of the drones blended perfectly with the chanter notes. Are you amazed how professional pipers seem to tune easily and get that steady full sound? What if I told you that it’s not just about good tuning?