Very memorable day yesterday, I got to load/shot one of these Ferguson Flint lock BP Rifles (replica) . Very cool.
Video shows the action..it was designed so you could load the rifle, while in battle, laying on your back. You drop and seat your ball ( .65) from the top, pour in the powder (65gr FFg) and then swing/turn the arm from underneath to close the breach.
https://www.youtube.com/watch?v=y85XEeOgfuQ
For more on the history of the rifle:
https://www.youtube.com/watch?v=5ODhQmE2OqY