Pellet (air gun)

Hornet Cal. 4,5mm (.177). Special pellet for hunting purposes. Lead with a point of brass. Extremely high penetrating power

Hunter Impact Cal. 4,5mm (.177). Pellet for hunting purposes. Lead with a point of synthetic polymers

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 ("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 head is usually sized to just touch the rifling, 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, 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 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. 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.

Eisenherz Cal. 4,5mm (.177). Plastic-coated pellet with a core of hard metal. For hunting purposes.

Plastic-coated pellets with a pointed steel core: Highest possible penetration power. Top: For rifles, bottom: for CO2-pistols with a revolver magazine

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

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 (FPS) of an airgun, which can result in greater accuracy.

However, lead-free pellets typically have a lower ballistic coefficient (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.[2]

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.[3]

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.