Surgical tubing may not be readily available or too expensive. I think most surgical tubing doesn't have the resistance to store much energy. It may be that layers of thick bicycle or car inner tube rubber would do a better job and be more accessible. The design of the assault slingshot uses kind of flat rubber strips, so it may work better. You know, another good thing about his design as opposed to finding a crossbow for modification is that everything in his design is replaceable or fashionable in somebody's house or garage away from prying eyes. If you have one guy loading while another guy aims and shoots I bet you can keep up quite a volley of fire. I wonder how accurate it actually is and if the accuracy could be improved by modifying it to have a type of barrel. Finally I wonder if the design could be modified to use spring steel instead of rubber for energy storage.