sorry bout before... thought you were talking about a coin roll down! HAHA! i've put the roll down on the back burner for a while... its really difficult for me.
but on another note... on the real subject.....
Try different size coins. You may be having difficulty because the size of the coin. When I was learning it I was trying to use quarters... and executing it properly wasn't go that fast.... then I switched to half dollars. When you get tired of dropping the coin switch to a different size. I found that the gold dollar was the fastes and easiest for me because of the way it fit on my fingers sizewize.
Don't give up... I practiced until my hand was sore.. and then practiced some more. I think I finally got it down after about a week of practice. I classify it as having it down when I can do it 20 times consecutively without dropping the coin. Quarters are still a bit slow for me though
The great thing is you can practice anywhere... driving, walking, sitting in a boring conference room listening to someone blab on and on for hours with out saying anything