In the UK, 0.177 inch (4.5 mm) caliber rifles are the most popular, as the higher velocity (relative to a .22” rifle of the same power) of the pellets means they fly with a flatter trajectory over the distances involved. One downside is that .177” pellets are very light and can be affected more by light crosswinds than the heavier pellets of a .22” (5.5 mm) rifle, in cases where .177 pellets and .22 pellets are traveling at the same initial muzzle velocity.