Difference between .177 and .220 pellets
Much higher velocities are being achieved with the .177 than with the .22 pellet
and as such provide flatter trajectories for increased accuracy. Pellets in the .22 calibre fly with more of a looped trajectory, and so they may require slight elevation adjustments, especially at range.
However, the benefit of the .22 pellet is its greater mass. This transfers more energy into the target, essentially increasing the force that the target is hit by. This is important for pest control as it ensures clean one hit kills, as opposed to .177 pellets that can pass straight through the animal due to their smaller size and faster speed.
What this essentially means is that .177 are more suited for target shooting. It is the calibre everyone uses in the Olympics, whilst the .22 is more suited to pest control.
Weight plays a similar role as calibre, with heavier pellets being more powerful but sacrificing a little accuracy thanks to having more of a looped trajectory. The pellets weight is measured in grain with 8-10gr being about average for .177 and 15-18gr being about average for .22.
The Best Caliber for Airgun Hunting? It’s Your Choice!
Ultimately caliber selection will depend on the quarry and situation. For small game you will usually find me carrying a .22 which will handle 90% of hunting needs.
I rarely use a .177 but have found the caliber to perform very well at closer ranges at lower energy levels to reduce the chance of over penetration. So there probably is no single best caliber for airgun hunting. They all have a place.