Target shotshells are used to break clays, while field shotshells are used for hunting.
Target loads are generally considered to cover shot sizes 9, 8, 7-1/2 and 7. Your choice of shot size will depend on the sporting regulations you are shooting within, the distance of your target, and the chokes in your shotgun. Due to the smaller shot size and therefore greater number of pellets per ounce, some shooters choose to shoot closer targets with smaller shot such as size 9. This ensures a better chance of connecting with the target. For longer targets a heavier, more massive shot is preferred due to its ability to carry momentum further than the lighter, smaller shot.