I think that world wide, the .177 is by far the most popular air rifle, likely outselling all others combined. With lower power restrictions elsewhere, the .177 can achieve a more reasonable velocity and trajectory, so it's easier to shoot. In the US, we want everything big, fast, and powerful. Unfortunately, we miss out on most of the 12 fpe rifles that are so sweet to shoot, with huge shot counts and virtually no noise. I de-tuned my .177 HW100 a couple of weeks ago, down to a little over 11 fpe, haven't refilled it yet! Great in the yard and still deadly on squirrels.