A pellet is a non-spherical

projectile A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found ...

designed to be shot from an

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 ...

, and an airgun that shoots such pellets is commonly known as a pellet gun. Air gun pellets differ from

bullet A bullet is a kinetic projectile, a component of firearm ammunition that is shot from a gun barrel. They are made of a variety of materials, such as copper, lead, steel, polymer, rubber and even wax; and are made in various shapes and constru ...

s and shot used in

firearm A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and operated by an individual. The term is legally defined further in different countries (see legal definitions). The first firearms originate ...

s in terms of the

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

s encountered; airguns operate at pressures as low as 50 atmospheres, while firearms operate at thousands of atmospheres. Airguns generally use a slightly undersized projectile that is designed to obturate upon shooting so as to seal the bore, and engage the

rifling Rifling is the term for helical grooves machined into the internal surface of a firearms's barrel for imparting a spin to a projectile to improve its aerodynamic stability and accuracy. It is also the term (as a verb) for creating such groov ...

; firearms have sufficient pressure to force a slightly oversized bullet to fit the bore in order to form a tight seal. Since pellets may be shot through a smoothbore

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 ...

, they are often designed to be inherently stable, much like the Foster slugs used in smoothbore shotguns.

Types

Diabolo pellet

The diabolo pellet (or " wasp waist pellet") is the most common design traditionally found in airguns. It consists of a solid front portion called the ''head'', which can have a flat (" wadcutter"),

hemispherical A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...

("round nose"), hollow point or conical ("pointed") front end profile, and a thin-walled funnel-shaped hollow rear portion called the ''skirt'', joined by an hourglass-looking narrow mid-section known as the ''waist'', giving the whole pellet the shape of a

diabolo The diabolo ( ; commonly misspelled ''diablo'') is a juggling or circus skills, circus juggling prop, prop consisting of an axle () and two cone, cups (hourglass/egg timer shaped) or cylinder, discs derived from the Chinese yo-yo. This object i ...

. The head is usually sized to just touch the

, and this keeps the pellet centered in the bore while keeping the friction as low as possible. The effect of friction is used in order to keep the pellet stationary until the piston has reached the end of its travel, compressing as much air as is possible. The thin hollow skirt is made of a malleable material, usually

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

, although non-toxic alternatives are available that use tin or even plastic. During shooting, the skirt flares out and obturates the bore when pressure builds up behind it to provide a good seal that allows efficient pellet acceleration, and engages the rifling whereby imparting spin. In a smoothbore barrel, the skirt will still flare to provide a tight seal, but since there is no rifling the pellet will not spin, and is less accurate. Because the majority of the pellet's mass resides in the solid head in the front, and the hollow skirt in the back generates significant drag during flight, this creates ''drag stability'' that will counteract yawing and help to maintain consistent trajectories. However, such stability is limited, and if the pellet's speed exceeds what the aerodynamics allow it will become unstable and start tumbling in flight. When this happens, the pellet can hit the target sideways and leave behind a keyhole-shaped impact hole on the target paper, instead of a clean round hole as expected from a direct frontal hit. This phenomenon is known as keyholing. Pellets are designed to travel at subsonic speeds. High velocities can cause light pellets to overly deform, or even break apart in flight. The transition from subsonic to supersonic velocities will cause almost all pellets to tumble. The closer a pellet gets to the

speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elasticity (solid mechanics), elastic medium. More simply, the speed of sound is how fast vibrations travel. At , the speed of sound in a ...

, the more unstable it becomes. This is a problem for high-powered "magnum" break-barrel and pre-charged pneumatic air rifles, which are capable of pushing lighter pellets beyond the

sound barrier The sound barrier or sonic barrier is the large increase in aerodynamic drag and other undesirable effects experienced by an aircraft or other object when it approaches the speed of sound. When aircraft first approached the speed of sound, th ...

. A few companies have addressed this issue by manufacturing heavier-than-normal pellets for use in these high powered air guns. The heavier weight of these pellets ensures lower muzzle velocities, resulting in less chance of tumbling and more overall accuracy. Their weight also makes them sectionally denser and less susceptible to wind deviation and drag deceleration, and thus imparts better external and terminal ballistic performance.

Ball pellets

The earliest airgun pellets are actually small round lead shots similar to those used in

musket A musket is a muzzle-loaded long gun that appeared as a smoothbore weapon in the early 16th century, at first as a heavier variant of the arquebus, capable of penetrating plate armour. By the mid-16th century, this type of musket gradually dis ...

s. First popularized by the Daisy BB Gun in the 1890s, a spring-piston airgun that shot "BB"-size birdshots, the .180-caliber lead shots were later replaced by the lighter .175-caliber steel shots modified from bearing balls, and remained popular as a plinking/ pest shooting projectile due to the popularity and affordability of

BB gun A BB gun is a type of air gun designed to shoot metallic spherical projectiles called BBs (not to be confused with similar-looking bearing balls), which are approximately the same size as BB-size lead birdshot used in shotguns ( in diameter) ...

s such as the Daisy Red Ryder. Modern BB guns use the same calibers as the pellet guns, namely the .177 caliber and (occasionally) .22 caliber. Galvinized/ copper-coated steel balls are the commonest projectile used in BB guns due to their better muzzle speed and penetration, but are only used in smoothbore

s due to the risk of

wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...

ing down

s, therefore lead balls are still used for rifled barrels.

Slug pellet

Recently, some manufacturers also have introduced the more cylindro-conoidally shaped "

slug Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...

" pellets for some of the more powerful modern PCP air rifles. Contrasted to the commonly used diabolo pellets, these slug pellets resemble Minié balls, with cannelures and a hollow base, and have more contact surface with the bore and hence need greater propelling force to overcome friction, but they have better

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 ...

s and thus longer effective ranges due to the more aerodynamic shape. Because these slug pellets have no skirts to generate enough drag stability in flight, they rely on spin stabilization from a fully rifled barrel.

Lead-free pellets

There are many different kinds of lead-free pellets, utilizing non-lead alloys and/or plastics in their construction. Consequently, they are much lighter than lead pellets, with weights ranging from 5.1 to around 20 grains. Due to their lighter weight, they accelerate more quickly inside the barrel, and commonly reach supersonic velocities. This increases the effective

feet per second The foot per second (plural feet per second) is a unit of both speed (scalar) and velocity (vector quantity, which includes direction). It expresses the distance in feet (ft) traveled or displaced, divided by the time in seconds (s). The corre ...

(FPS) of an airgun, which can result in greater accuracy. However, lead-free pellets typically have a lower

(BC), which results in more wind-drift, and reduced velocity at longer distances. As an example, H&N Sport's Baracuda Green pellet has a BC of 0.013, but the standard Baracuda pellet's BC is 0.024. Although some airguns are equipped with moderators or other noise dampening chambers, lead-free pellets can break the sound-barrier, and produce a loud cracking noise. This can be misinterpreted as a malfunction of the suppressor, when in fact it results from using a supersonic pellet. Upon switching back to a lead pellet, the supersonic crack will cease. H&N Sport markets their lead-free pellets as part of their "GreenLine," and Gamo markets their lead-free pellets as a "Performance Ballistic Alloy" (PBA). Regardless of the terminology, the underlying technology involves a mix of non-lead materials, such as zinc, iron, tin, or copper. Lead-free pellets are offered by all major manufacturers, including RWS, Gamo, H&N Sport, Predator International, JSB, Crosman, SIG Sauer, and others. These metals are all lighter than lead, and significantly harder. As a result, they penetrate more deeply, and do not deform as greatly upon impact with the target. By contrast, lead pellets are often designed to fragment, expand, or mushroom, and can cause more damage. As a result, they are favored by hunters. However, many hunters are using non-lead pellets, to avoid lead contamination.

Match shooting use

Match pellets are used for the 10 metre air rifle and 10 metre air pistol disciplines. These calibre pellets have wadcutter heads, meaning the front is (nearly) flat, that leave clean, hole punch-like round holes in paper targets for easy scoring. Match pellets are offered in tins and more elaborate packagings that avoid deformation and other damage that could impair their uniformity. Most match pellets are made of soft lead (a

alloy with low

antimony Antimony is a chemical element; it has chemical symbol, symbol Sb () and atomic number 51. A lustrous grey metal or metalloid, it is found in nature mainly as the sulfide mineral stibnite (). Antimony compounds have been known since ancient t ...

content), but some companies offer lead-free versions. The antimony content is used to control the hardness of the soft lead alloy. It is a very soft alloy, which makes it easy to process. Since the soft lead alloy is prone to strongly deform when striking a bullet catcher, it rapidly loses its kinetic energy and will not easily bounce off. Lead is toxic and hazardous to the environment, so precautions should be taken if shooting with lead pellets. For this reason, many shooters use lead-free match pellets, produced by H&N Sport, Predator International, JSB, RWS, Olympia Shot, Gamo, or Daisy. Match air gun shooters are encouraged to perform shooting group tests with their gun clamped in a fixed rest in order to establish which particular pellet type performs best for their air gun. To facilitate maximum performance out of various air guns the leading match pellet manufacturers produce pellets in graduated weight variants (the light/high speed variants are often marketed for air pistol use) and with graduated "head sizes", which means the pellets are offered with front diameters from up to . However at higher and top competitive levels, even these variations are thought too coarse-grained and match pellets are ''batch tested''; that is, the specific gun is mounted in a machine rest test rig and pellets from a specific production run on a specific machine with the same ingredients fed into the process (a ''batch'') are test-fired through the gun. Many different batches will be tested in this manner, and the pellets which give the smallest ''consistent'' group size without fliers (shots which fall outside of the main group) will be selected (small but inconsistent group sizes are not useful to a top competitor); and the shooter will then purchase several tens of thousands of pellets from that batch. Group sizes of diameter are theoretically possible, but practically shot groups of are considered highly competitive.Haendler & Natermann Finale Match Rifle
/ref> Unbatched ammunition, especially if the air gun is not regularly cleaned, is generally thought to be capable of only diameter group sizes. Batch testing match pellets for a particular gun is not generally thought to be worthwhile until the shooter reaches a high proficiency level, around the 95% level (570 for men, 380 for women).

References

External links

{{Commons category inline, Air gun pellets Pneumatic weapons Projectiles