Building a reliable RBG is significantly harder than building a static Lego set. Because Lego bricks are plastic, friction is the enemy. If the mechanism is too tight, the rubber band snaps or jams. If it is too loose, the band falls off before firing.
Sites like Brick-Guns provide detailed instructions for iconic movie and video game weapons. Pro Tips for Builders lego rubber band guns
Far from being simple toys, high-level Lego RBGs are marvels of mechanical engineering, utilizing the precision of the stud-and-tube system to create everything from simple repeaters to fully automatic Gatling guns. Building a reliable RBG is significantly harder than