I shoot only .177, years ago taking a short plunge into .20. While the discussion is mildly interesting I find that it doesn't sway my beliefs a bit. And that goes as follows. My primary use for air rifles is small pests and casual trigger time to keep me sharp for modern firearms. There is no typical small pest of interest to me that the .177 has failed to dispatch so I know the energy is adequate and in many cases more than needed. It doesn't take huge energy to dispatch a grackle. More important to me is the time it takes the shot to reach the target. Especially at distances wary targets like to keep to be comfortable, the sound of the shot can reach them long before the shot does. This gives them time to react to the shot and cause a miss so I'll take velocity over energy at the target any day.
Placing that shot is also important and that leads me back to the .20. Back in the day I liked the idea of the .20 as a compromise between with energy and velocity worlds. My trial was with a field/target R1 and I spent an entire summer trying to learn the rifle. Burned money on pellets and time, the rifle was a very accurate shooter, as would be expected. When ever I took the rifle to the field, however, I missed way more than I hit. I'd go back, verify zero, and try again, still missing at the varied distances of targets in the field. Ultimately I came to believe that the trajectory and velocity were just enough different than what I'd been shooting for a decade at the time that I wasn't adapting to it. Just couldn't learn the ability to on-the-spot determine aiming corrections for pop up targets from as short at five yards out to fifty with a 35 yard zero.
I sold that rifle and have never looked into another caliber. Today there are rifles (PCP) that can make .177 velocities with .22 cal fodder and those I imagine I could do well with. But that takes me back to my current use of the rifles and I cannot justify a new and expensive gun to do exactly what I'm doing with the guns I currently have. Some of the comparisons above are interesting, though. Especially where .177 and .22 seem to perform the same in places.
