I had the same issue on mine. Tried moving the coil lower to introduce some slack but still wasn't 100% and would sometimes fall back down the popper as well. Plus I really didn't like the way coil jumped because of the slack, bound to cause problems with wires breaking off, etc.
What worked for me was putting a piece of gorilla tape (really strong duct tape) inside the popper about 4 inches deep from the exit hole. Now the ball reliably ends up in the gun and is much quieter too. Sometimes the simplest solution is also the best. 
Matthews, NC
