You should print everything with minimum 3 shells and 20-30% infill and the chamber for the projectile with 5 shells and 90 % infill. The GripRubber file should be printed with rubber-material, but can also be printed with other materials. The Light.stl should be printed with transparent material if you want to add a LED. The ProjectileBodyWithArms.stl should be printed with supports just under the arms and the upper rings. If your slicer automatically makes support behind the arms, remove them in your slicer programm or add manually the needed support. You also need support for the most parts, some more, some less. The files are all pre-aligned for your printbed to get the best look out of the parts.