.177 caliber or 4.5 mm caliber is the smallest diameter of pellets and BB shots widely used in

air gun An air gun or airgun is a gun that uses energy from compressed air or other gases that are mechanically pressurized and then released to propel and accelerate projectiles, similar to the principle of the primitive blowgun. This is in contr ...

s, and is the only caliber generally accepted for formal target competition. It is also sometimes used for hunting small game, like

fowl Fowl are birds belonging to one of two biological orders, namely the gamefowl or landfowl ( Galliformes) and the waterfowl ( Anseriformes). Anatomical and molecular similarities suggest these two groups are close evolutionary relatives; toget ...

. It is also used in

field target Field target is an outdoor airgun field shooting sport. Competitions are usually fired at self indicating steel targets placed between . There are two classes; ''Piston'' for spring-piston air guns, and ''PCP'' for pre-charged pneumatic air gu ...

competitions, where it competes with .20 caliber (5 mm) and .22 caliber (5.6 mm) rifles. Steel BBs are typically slightly smaller than lead BBs at diameter, although the bore diameter of the

barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden stave (wood), staves and bound by wooden or metal hoops. The word vat is often used for large containers ...

are the same. Some air guns are designed to accept .177 pellets, .177 lead shot, or .175 steel BBs interchangeably.

Relationship between caliber and trajectory

If two guns fire pellets of different weights, the gun firing the lighter pellet must fire it at a higher velocity to achieve the same

muzzle energy Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle (firearm), muzzle of a firearm. Without consideration of factors such as aerodynamics and gravity for the sake of comparison, muzzle energy is used as a rough indi ...

. This is an important consideration in locations where air guns are legally restricted by muzzle energy. Because a .177 pellet is lighter than a larger caliber pellet of similar design, the .177 pellet can be propelled faster and therefore on a flatter

trajectory A trajectory or flight path is the path that an object with mass in motion follows through space as a function of time. In classical mechanics, a trajectory is defined by Hamiltonian mechanics via canonical coordinates; hence, a complete tra ...

, without exceeding the legal limit on energy. However, because the lighter projectile has a lower

ballistic coefficient In ballistics, the ballistic coefficient (BC, ''C'') of a body is a measure of its ability to overcome air resistance in flight. It is inversely proportional to the negative acceleration: a high number indicates a low negative acceleration—the ...

, it loses its initial energy to air resistance faster than a heavier, slower pellet. Therefore, a heavier pellet (typically of a larger caliber) may be preferred for hunting.

External links

Information on .177 air rifle pellets

Information on .177 pellets

Relationship between caliber and trajectory

External links

See also