Quoted from RobT:
I would definitely try to fix that 1/2 gap between the ball and plunger. That can definitely have an impact on how much velocity the ball has when hit by the plunger.
Yes, I'll have to look at the mech more closely to see what's going on. I was first trying to determine if the gap was normal or not. I assume it's supposed to be like it is on AC/DC cannon, where the ball rests directly on the plunger.