Ballistic experiment for home and school

The trajectory of a projectile launched under a certain angle at a certain speed can be calculated. However, it is much more fun to do a real ballistic desktop experiment.
We need a launch tube which can be set under an angle of choice, a projectile and a power source. In this Thing we use two standard 5mm ballpoint springs.We change the launch angle and measure the distance. The central question: At what angle is the distance at its maximum (don't shoot the cat).
https://youtu.be/UUE75MVYqds