To use it, one holds the bottom of the frame, and sights through the fork. One places the projectile (usually a small stone or metal ball) into the pocket. Then one grasps the projectile through the pocket, and pulls back against the rubberbands, stretching the rubber bands between the pocket and the frame. When one releases the pocket, the stretched rubber bands accelerate the pocket, and projectile.
A related technique is to aim by aligning the elastic bands with the target.
A slingshot champion appearing on the David Letterman Show some years ago said to hold the projectile pocket at a fixed position near the body, such as the hip, and move the frame based on gut feeling and practice, just like a gunslinger or hip-shooter in the American wild west. Many gunslingers could hit a target without raising their weapon to eye level.
The lighter the projectile, the faster it will move, and the more damage it will create. Small metal balls weighing about two gramss are best.
With practice, slingshots are effective against small rodents and songbirds at ranges up to 25 meters. They are excellent for hunting rats and pigeons. Because of the low ammunition cost (pebbles work) and ease of use, slingshots are very popular with boys.
The weak hand holding the frame becomes fatigued by doing so. The best slingshots have a wrist-brace so the user's weak hand doesn't have to hold the frame very tightly.
The material for the rubbers is critical. The best widely-available material is latex rubber surgical tubing. It lasts about six months before it needs to be replaced. It can be attached to the frame and packet by stretching it over a metal rod of the correct diameter. Some slingshots have been constructed of metal tubing of the exact diameter. Rubbers should be stored under water away from sunlight to protect them from the air's ozone, which causes them to stiffen and crack.
The weight of the pocket is critical, because if the pocket is very heavy, the slingshot will be weak. The best pockets are made of soft leather, which does not fray.
Securely attaching a pocket at home can be quite difficult. An effective way is to drill a short section of hardwood dowel lengthwise, and place the pocket in a cotter pin. Next, insert the pin into the dowel, and wrap the ends of the pin completely around the dowel. Finally, stretch the rubber over the dowel and pin-ends. Never reuse a cotter pin.
The slingshot is not related to the sling. Mechanically it operates on a different principle. Operation is different, as well.
Today, slingshots are used at paintball games as backup or silent sniper weapon. On some playfields they are even banned for sending the paint bullet faster than the allowed 300 feet/second, which is considered an unsafe and unfair advantage. Source - newsgroup rec.sport.paintball .
See also gravitational slingshot.