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 i ...

designed to be shot from an

air gun An air gun or airgun is a gun that fires projectiles pneumatically with compressed air or other gases that are mechanically pressurized ''without'' involving any chemical reactions, in contrast to a firearm, which pressurizes gases ''chemical ...

, 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. Bullets are made of a variety of materials, such as copper, lead, steel, polymer, rubber and even wax. Bullets are made in various shapes and co ...

s and shot used in

firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...

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 a ...

s encountered; airguns operate at pressures as low as 50 atmospheres, while firearms operate at thousands of

atmospheres The standard atmosphere (symbol: atm) is a unit of pressure defined as Pa. It is sometimes used as a ''reference pressure'' or ''standard pressure''. It is approximately equal to Earth's average atmospheric pressure at sea level. History The s ...

. Airguns generally use a slightly undersized projectile that is designed to obturate upon shooting so as to seal the bore, and engage the

rifling In firearms, rifling is machining helical grooves into the internal (bore) surface of a gun's barrel for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting to stabilize the ...

; 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 A smoothbore weapon is one that has a barrel without rifling. Smoothbores range from handheld firearms to powerful tank guns and large artillery mortars. History Early firearms had smoothly bored barrels that fired projectiles without signi ...

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 staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, ...

, they are often designed to be inherently stable, much like the

Foster slug A shotgun slug is a heavy projectile made of lead, copper, or other material and fired from a shotgun. Slugs are designed for hunting large game, and other uses, particularly in areas near human population where their short range and slow speed h ...

s used in smoothbore shotguns.

Types

Diabolo pellet

The diabolo pellet (or "

wasp waist Wasp waist is a women's fashion silhouette, produced by a style of corset and girdle, that has experienced various periods of popularity in the 19th and 20th centuries. Its primary feature is the abrupt transition from a natural-width rib cag ...

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 ("round nose"),

hollow point upright=0.2, Cross-section of a hollow-point bullet; proportions are those of a .22 Long Rifle cartridge Jacketed soft point (JSP) round. Right: Jacketed hollow-point (JHP) round. JSP is a semi-jacketed round as the jacket does not extend to ...

conical A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines c ...

("pointed") front end profile, and a thin-walled

funnel A funnel is a tube or pipe that is wide at the top and narrow at the bottom, used for guiding liquid or powder into a small opening. Funnels are usually made of stainless steel, aluminium, glass, or plastic. The material used in its construct ...

-shaped hollow rear portion called the ''skirt'', joined by an

hourglass An hourglass (or sandglass, sand timer, sand clock or egg timer) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated flow of a substance (historically sand) ...

-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 prop consisting of an axle () and two cups (hourglass/egg timer shaped) or discs derived from the Chinese yo-yo. This object is spun using a string attached to two hand ...

. 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 with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...

, 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 Seal may refer to any of the following: Common uses * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to imp ...

that allows efficient pellet acceleration, and engages the rifling whereby imparting spin. In a

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 The following are terms related to firearms and ammunition topics. A *Accurize, accurizing: The process of altering a stock firearm to improve its accuracy. *Action: The physical mechanism that manipulates cartridges and/or seals the breech ...

. 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 elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as we ...

, 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 Muzzle velocity is the speed of a projectile (bullet, pellet, slug, ball/shots or shell) with respect to the muzzle at the moment it leaves the end of a gun's barrel (i.e. the muzzle). Firearm muzzle velocities range from approximately to i ...

, 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.

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 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 shell, or only a ...

" 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 correspond ...

(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 with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient ti ...

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