Joerg Sprave is a creative guy. He's also an ambitious one. That's why, when his YouTube viewers doubted that his slingshot rifles were actually rifles—after all, they're slingshots—he set out to prove them wrong with a big piece of sewage tube.
Of the many unique things about a rifle, the grooved (or "rifled") barrel that makes the bullet spin is key, ensuring that a bullet flight will be straight and stable. Joerg's slingshot cannons didn't have barrels at all, however, which is why his viewers called him out. Using a length of PVC pipe and a drill, he managed to build a fast spinning barrel that thus rotates the ball bearing projectile inside, even though the round ball would fly fine on its own. In Joerg's own words, "What is it good for? Nothing." Nothing!? Say that after you've used it to defend your home. [YouTube]