Generally, slower pellets are more accurate than fast pellets. This is particularly true if the pellet is traveling faster than the speed of sound. The shock wave produced by the pellet will interfere with its flight, causing it to veer off target. For competition target shooting, pellets usually travel around 550 feet per second.
If you are using a high-powered air gun, then choose heavier pellets to bring down the speed of the pellet through the air and increase accuracy. Some examples of heavy (high grain) pellets are the Crosman Premier (at 10.5 grain), the Gamo Magnum (at 8.5 grain) and the RWS Super-H Point (at 7.4 grain).
The wadcutter pellet design is the choice for precision competition shooting. Wadcutter pellets are designed to fire at a lower velocity to increase accuracy. They have a flat surface to produce more drag and to cut a smooth hole in the target for easy scoring. These pellets may also be used for hunting and pest control.