Some guns pattern 2.75" loads as well, or better, than 3" loads. Fewer pellets in the shell don't necessarily translate to fewer pellets on the target. You've got fewer pelletscrowding through your tight choke so there's less opportunity for pattern blowing pellet deformation. The velocity of the shorter loads often exceeds the longer loads. They have about the same amount of powder. A lighter payload makes for a faster delivery.