The .177 Caliber Airgun
The .177 caliber was probably created shortly after the start of the 20th century. It seems to have surfaced first in England. The advantage of .177 is a smaller pellet that uses less material, usually lead. It is widely used for general shooting and is the only caliber that can be used for bullseye target shooting anywhere in the world. The rules of all official shooting organizations mandate a .177 caliber gun for both pistol and rifle competition. Because of this, the popular misconception is that the .177 is somehow more accurate than the other three calibers. This is not strictly true, but since all target airguns are made in this caliber only, a lot of .177 guns are more accurate than guns in other calibers.
The sport of field target is one competitive shooting sport in which a .177 places the shooter at a distinct advantage. The shooter must shoot a pellet through a small hole in a steel target to hit a paddle, knocking the target down and registering a hit. If the pellet touches the side of the hole there is a good chance the target will not fall and no point will be awarded. The kill zone holes range from 1/4-inch to 2-inches in diameter, but the smaller holes are by far more common in a match. So the smaller size of the .177 pellet makes it the statistically superior choice in this sport.
A problem .177 pellets have is that their light weight allows them to go faster than the larger sizes. Once the speed of the pellet approaches the speed of sound, a variable speed of approximately 1,100 f.p.s. at sea level, the accuracy suffers. So, for powerful air rifles, shooters must select the heaviest pellets in .177 to keep the velocity down.
Sometimes air guns come in both .177 and .22 calibers. Any given airgun will shoot faster in .177 than in .22 if all things are equal. That same airgun will hit about 20 percent harder in .22. The .177 pellets tend to be less expensive than .22 pellets, plus there are often more of them in a box. The .22 pellet is larger and some people find it easier to load than the smaller .177.