That is right, I made a slingshot release in the tradition of a medieval bihander sword.
This is a release that you can use to shoot cannon balls (max. caliber 80mm = 8cm = 2.15").
You simply need a length of Thera Band, and either two poles or two fearless assistants that hold the ends of the rubber bands. Then you clamp your ammo into the release and walk backwards as far as you can.
Then you press with both thumbs on the release and the shot falls.
This can be as powerful as the cannon I made a while ago. You have to use a lower draw weight, but you can compensate by using a longer draw length. Use bands that are three feet long, and you can stretch them to 15 feet easily.
A dangerous little thingy, in fact. Suppressive governments (and Zombies) beware. A new breed of slingshots is approaching.
(Slingshot has been included into the pic just to show the dimensions)