[Ernst]

Is the bucket that the ball rests in just a bucket, or is it some kind of pneumatic suction cup?

I would consider either replacing it with a different shaped bucket that has longer guides to set the ball's trajectory, or just adding additional guides after the bucket ends. In the video you showed, they would go on the left side and curve up to better cradle the ball while firing. We use a catapult on our robot this year and have had very good results with a curved bucket. Instead of just pushing the ball out, the ball rolls off. This would definitely change your hard stop and release point, but I think it could take out some of the variability from the balls deflecting differently.