I won't join a circus to find out so this task goes to you Matt, you find the answer to nearly anything we experience in day-to-day life. What propels the human cannonballs? I don't believe it is a powerful explosive charge. That's for effects. Not a spring, maybe a giant and long bungee, compressed air, steam (catapult), or hydraulics. These are my likely guesses. I can hardly wait to find out.
-- Curious Greg Gieselman in Point Loma/OB
Well how did you know that Grandma comes from a long line of circus folk? We have these cute pictures of Grandma practicing riding a bicycle across a high wire, having a little trouble with her training wheels, though. As a teenager she was swept off her feet by a trapeze artist, but gave up the career when he accidentally dropped her into the elephant pen. But she still gets teary when she sees a big top. And she can tell you without a doubt that no gunpowder is involved in the human cannonball trick, except as special effects. The living projectile hops into a cylinder that slides down inside the barrel. At the base of the barrel is a container of compressed air set at about 150 psi. The release of the air shoots the cylinder down the barrel, it stops before it's ejected, but of course the human bean keeps going. It might seem like the tricky part is over, but more human projectiles are injured or killed by missing the landing net than by an problems from the concussion. It's a tricky business. The first human cannonball was a woman in a circus in England, and she used a contraption made of springs and wires.