If both caliber air rifles have the same muzzle velocity, say, 495 fps if they are both non-PAL or no licence required rifles, they would both have the same trajectory. If both rifles required a PAL to purchase, the .177 would most likely have the greater MV and hence the flatter trajectory, which lends itself to more accurate shooting at longer distances. Keep in mind that any pellet rifle that shoots over about 950 fps will suffer from pellet instability as the pellet approaches the trans sonic zone. Generally speaking .177 air rifles and air pistols are favoured for target shooting because they are flatter shooting. Not only that it is easier to find good quality pellets in .177 than in .22, and the vast majority of pellet guns, rifle or pistol, have a preference for a certain shape, size, and weight of pellet. Pellets come in different head sizes. For example .177 comes in 4.50, 4.51, 4.52, and 4.53 head sizes (at least in the better pellets such as JSB Exact and H&N Field Target Trophy. Round head pellets are best for longer distances and are equally accurate as wadcutters at shorter distances.