A couple guys in our gun club have built them, they shoot them off at out club picnic every year. They built theirs more like mortars, though. They're really impressive.
They use, I believe, one cup of black powder. Not sure about that or the burn speed, though.
The launch them vertically with a slight angle towards the direction they want to ball to go. They aren't very loud when launched, but as the ball flies and rotates, the finger holes make a whistling sound "HOO-HOO, HOO-HOO, HOO-HOO" all the way up and back down. They go about 300 yards downrange and at least that high up. As they fall they whistle coming down too, like bombs in old WWII movies. They hit the the ground with a thud and dirt flies up a bit, you usually find the ball a couple feet in the ground. The balls can be used over and over but sometimes they do break apart on impact.