From power plants and pellet shapes to optics and ballistics vocabulary, this glossary covers the terms you'll run into shopping for or shooting an airgun. Where a term ties into one of our calculators, we've linked straight to it.
Accuracy
How closely a pellet's point of impact matches the point of aim, shot after shot. Distinct from precision (tight groups that may all miss the same direction) though the two terms get used loosely.
Adjustable Comb
A stock's cheekpiece that raises or lowers so your eye lines up consistently with the scope, regardless of scope height or tube diameter.
AO (Adjustable Objective)
A ring on the scope's objective (front) lens that corrects parallax at different distances. See Parallax.
Air Rifle
Any rifle that propels a projectile with compressed air or gas rather than a chemical propellant charge, covering spring-piston, PCP, CO2, and pump-pneumatic designs.
Air Stripper
A muzzle device on some PCP guns that vents excess air away from the pellet as it leaves the barrel, intended to reduce the "crack" of muzzle report.
Ballistic Coefficient (BC)
A number describing how well a pellet resists air drag in flight, combining its sectional density with its shape. Higher BC means the pellet sheds velocity more slowly. See Sectional Density, its exact, calculable half.
Barrel Droop
A slight downward bend in a barrel (common on some break-barrels) that shifts the point of impact and can require extra scope elevation or a shimmed mount to correct.
BB
A small, round, typically steel projectile used in smoothbore BB guns, distinct from diabolo-shaped lead or alloy pellets fired from rifled airgun barrels.
Big Bore
Airguns firing calibers larger than the common .177–.25 range, typically .30 caliber and up, built for hunting larger game with airgun-scale energy.
Break-Barrel
A spring-piston or gas-ram rifle cocked by hinging the barrel downward, which compresses the internal spring or piston. No air tank or CO2 needed.
Bullpup
A rifle layout where the action and magazine sit behind the trigger group, inside the buttstock, shortening overall length without shortening the barrel.
Buddy Bottle
A smaller carbon fiber or steel air cylinder used to top off a PCP gun's onboard reservoir in the field, refilled itself from a larger tank or compressor at home. See our Tank Fill Calculator.
Caliber
A pellet or barrel's bore diameter, most commonly .177 (4.5mm), .20 (5mm), .22 (5.5mm), or .25 (6.35mm) in airguns, with big bore calibers running larger still.
Carbine
A shorter, lighter-barreled version of a rifle, generally easier to maneuver at the cost of a small amount of velocity compared to the full-length version of the same gun.
Chronograph
A device that measures a pellet's velocity as it passes two sensors a known distance apart, giving you the fps number needed for calculators like our FPE Calculator.
CO2
Compressed carbon dioxide, typically supplied by disposable 12-gram cartridges, used as the power source in CO2 airguns. Performance shifts noticeably with outdoor temperature.
Cocking Effort
The force needed to cock a spring-piston or gas-ram gun, usually measured in pounds. Higher-powered springers generally need more cocking effort.
Cocking Lever
The arm used to compress a spring-piston or gas-ram powerplant, most often the barrel itself (break-barrel), a lever under the barrel (under-lever), or a lever on the side of the action (side-lever).
Crown
The finished edge at the muzzle end of the barrel. A damaged or uneven crown can noticeably hurt accuracy, since it's the last surface guiding the pellet as it leaves the bore.
Detent
A small spring-loaded ball or catch, commonly used to hold a break-barrel closed, or to hold a pellet in the breech before firing.
Diabolo
The classic waisted, skirted pellet shape (narrow at the middle, flared at the base) used by the vast majority of airgun pellets. The shape stabilizes the pellet in flight without needing rifling-driven spin alone.
Dieseling
A small ignition of oil vapor inside a spring-piston gun's compression chamber, caused by the heat of rapid compression. Produces a sharper crack and puff of smoke; a normal, if messy, part of some springers' break-in.
Dot Sight
A non-magnifying optic that projects an illuminated dot onto a lens, used for fast target acquisition at close range rather than precision distance shooting.
Domed Pellet
A pellet with a rounded, aerodynamic nose, generally the best all-around choice for retaining velocity and accuracy at distance compared to flat or pointed noses.
Dry-Fire
Firing a gun without a pellet loaded. Not recommended on spring-piston guns specifically, since the piston can slam forward with nothing to absorb the impact, risking damage over repeated dry-fires.
Elevation Turret
The scope adjustment dial (usually on top) that moves point of impact up or down, typically in clicks representing fractions of an MOA or mil at 100 yards.
Eye Relief
The distance your eye needs to be from the scope's rear lens to see a full, clear sight picture. Springers in particular need generous eye relief, since the gun recoils toward the shooter on firing.
Field Target (FT)
A precision shooting discipline where competitors shoot at metal knockdown targets with a hole (the "kill zone") at varied, unmarked distances, testing both marksmanship and range estimation.
Fill Pressure
The pressure (in PSI or bar) a PCP gun's reservoir needs to be filled to for full power and shot count, specified by the manufacturer. Central to our Tank Fill Calculator.
Fill Probe
The fitting used to connect a fill tank or pump to a PCP gun's reservoir. Probe types vary by manufacturer, which is why fill probes aren't universally interchangeable.
Firearms Certificate (FAC)
In the UK, a license required to own airguns above certain power thresholds (commonly cited around 12 ft-lbs for rifles, 6 ft-lbs for pistols). Power limits and licensing requirements vary by country and region, always check current local regulations.
Foot-Pounds of Energy (FPE)
The kinetic energy a pellet carries at the muzzle, combining weight and velocity into one number. See our FPE Calculator for the full formula and typical FPE by use.
FPS (Feet Per Second)
A pellet's muzzle velocity. High FPS alone doesn't tell you much without weight factored in, which is why FPE is the more useful power comparison. See our FPS Calculator.
Gas Ram (Gas Piston)
A break-barrel or lever power plant that uses a sealed, compressed-gas strut instead of a coiled steel spring. Generally smoother-shooting and safer to leave cocked than a coiled spring, at a higher price.
Grains
The unit of weight used for pellets (and bullets), with 7,000 grains equal to one pound. Used directly in both the FPE and SD calculators.
Group / Grouping
The overall spread of several shots fired at the same point of aim, usually measured center-to-center between the two widest hits. Smaller groups indicate better precision from the gun, pellet, and shooter combined.
Hammer
In a PCP gun, the internal component that strikes the valve open to release a metered burst of air behind the pellet when the trigger is pulled.
Hand Pump
A manual, multi-stage pump used to fill a PCP gun's reservoir without a tank or compressor, at the cost of considerably more physical effort per fill.
HFT (Hunter Field Target)
A field target variant shot from realistic field positions (kneeling, standing, sitting) rather than a fixed benched or prone position, closer to simulated hunting conditions.
Holdover
Aiming above the actual target to compensate for pellet drop at distance, as an alternative to dialing the scope's elevation turret.
Hop-Up
A mechanism (mainly on smoothbore BB and airsoft-style guns) that imparts backspin on the projectile to extend its effective range through the Magnus effect.
Iron Sights
Fixed or adjustable metal front and rear sights built into the gun itself, used without an optic. Also called open sights.
Lead-Free Pellet
A pellet made from an alloy (often tin or a similar metal) instead of lead, used where lead ammunition is restricted or by choice for hunting. Generally lighter than a lead pellet of the same size, which changes its trajectory.
Lock Time
The delay between the trigger releasing and the pellet actually leaving the barrel. Shorter lock time reduces the window for the shooter to move off target before the shot fires, particularly relevant on springers.
Magazine (Mag-Fed)
A rotary or linear cartridge holding multiple pellets, allowing repeat shots without manually loading each one into the breech.
Mainspring
The coiled steel spring that powers a spring-piston gun, compressed on cocking and released on firing to drive the piston forward.
Mil-Dot
A scope reticle marked with dots or hashes spaced in milliradians, used for both holdover and estimating range based on a target's known size.
Milliradian (Mil)
An angular unit used in some scope reticles and turrets, where 1 mil subtends roughly 3.6 inches at 100 yards. An alternative system to MOA; most scopes use one or the other, not both.
MOA (Minute of Angle)
An angular unit equal to 1/60th of a degree, subtending roughly 1.047 inches at 100 yards. Used for scope adjustments and describing group size independent of distance.
Multi-Pump Pneumatic
A gun powered by manually pumping an onboard lever several times before each shot, building air pressure with no tank, CO2, or spring involved.
Muzzle Brake
A device at the muzzle that redirects escaping air or gas, sometimes used to reduce report or perceived recoil. On many airguns this is largely cosmetic given the low recoil involved.
Muzzle Energy
See Foot-Pounds of Energy (FPE), the standard way this is expressed for airguns.
Muzzle Velocity
See FPS, a pellet's speed as it leaves the barrel.
Nitro Piston
A branded term for a gas-ram power plant, functionally the same sealed-gas-strut design regardless of manufacturer naming.
Non-Regulated (Non-Reg)
A PCP gun without a pressure regulator, meaning shot-to-shot velocity gradually declines as the reservoir empties, compared to a regulated gun's more consistent velocity curve.
O-Ring
A small rubber or synthetic seal used throughout a PCP gun's valve and reservoir to keep pressurized air contained. A common wear part responsible for air leaks over time.
Objective Lens
The front lens of a scope, facing the target. Its diameter affects light-gathering and, on adjustable-objective scopes, parallax correction.
Over-Lever
A less common cocking mechanism using a lever above the action, distinct from under-lever and side-lever designs.
Parallax
An apparent shift in the reticle's position on target as your eye moves off the scope's optical center axis, more pronounced at close range through high-magnification scopes. Corrected with an AO ring or side focus turret.
PCP (Pre-Charged Pneumatic)
A gun that stores compressed air in an onboard reservoir, filled ahead of time from a tank, pump, or compressor, delivering multiple shots per fill. See our Tank Fill Calculator.
Pellet
The projectile fired from rifled airgun barrels, most commonly diabolo-shaped, distinct from round BBs fired from smoothbore barrels.
Pellet Trap
A backstop designed to safely catch and contain pellets, ranging from simple bag traps to steel traps rated for higher-power guns.
Penetration
How deeply a pellet travels into a target, influenced by weight, velocity, shape, and construction. Related to but distinct from raw energy, a fast light pellet and a slower heavy one can carry the same FPE while penetrating differently.
Piston
In a spring-piston or gas-ram gun, the component driven forward by the spring or gas strut, compressing air in the chamber ahead of it to push the pellet down the barrel.
Plinking
Informal, low-stakes shooting at cans, targets, or other reactive objects, generally for fun rather than competition or hunting.
POA / POI (Point of Aim / Point of Impact)
Where the sights are aimed versus where the pellet actually lands. Sighting in (zeroing) brings these into alignment at a chosen distance.
Pointed Pellet
A pellet with a sharp, tapered nose, associated with deeper penetration on small game compared to a domed or flat-nosed pellet of the same weight.
Power Plant
The mechanism that propels the pellet, broadly spring-piston, gas-ram, PCP, CO2, or multi-pump pneumatic.
Pull Weight (Trigger)
The amount of force needed to release the trigger and fire the gun, usually given in pounds or ounces. Lighter, crisper pull weights generally aid accuracy.
Rail (Scope Rail)
The mounting surface on top of the receiver, most commonly an 11mm dovetail or Picatinny/Weaver rail, that a scope mount clamps onto.
Recoil
The rearward (and on some springers, complex two-way) movement of the gun on firing. Spring-piston guns generally have more pronounced recoil behavior than PCP or CO2 guns of similar power.
Regulator (Reg)
A component in some PCP guns that meters air from the main reservoir down to a fixed, consistent pressure before it reaches the valve, extending the number of shots at consistent velocity per fill.
Reservoir
The onboard air storage of a PCP gun, filled from an external tank or pump. Its size in cc is a key input in our Tank Fill Calculator.
Retained Velocity
A pellet's velocity at some distance downrange, always lower than muzzle velocity due to drag. Ballistic coefficient describes how quickly that velocity is lost.
Rifling
Spiral grooves cut into a barrel's bore that impart spin on the pellet, stabilizing it in flight. Twist rate describes how tight that spiral is.
Scope
A magnifying optic mounted on the gun for aiming. Airgun-rated scopes are often built to handle the two-way recoil of spring-piston guns specifically, unlike scopes designed only for firearms.
Scope Creep
A scope gradually sliding forward or backward in its mount under repeated recoil, throwing off eye relief and zero over time. Common on springers with worn or under-tightened mounts.
Sear
The internal catch that holds the piston (springer) or hammer (PCP) under tension until the trigger releases it.
Sectional Density (SD)
A pellet's weight relative to its cross-sectional area, an exact, easily calculated measure of how well it carries its weight through a given diameter. See our Sectional Density Calculator.
Shot Count
The number of usable shots a PCP gun delivers per fill before velocity drops off. Affects how many fills a given tank will actually cover; see our Tank Fill Calculator.
Shroud
A sleeve surrounding the barrel, often housing a sound-dampening baffle system, used to reduce muzzle report on PCP guns.
Side-Lever
A cocking mechanism using a lever on the side of the action rather than the barrel or an under-barrel lever, common on some PCP repeaters as well as springers.
Sight-In
See Zero, the process of adjusting the scope so point of aim matches point of impact at a chosen distance.
Silencer / Moderator / Suppressor
A device that reduces muzzle report by slowing and cooling escaping air or gas. "Moderator" is the more common term in the UK, "suppressor" and "silencer" are used more interchangeably elsewhere. Legal status varies significantly by country and region for airguns specifically, always check local regulations before adding one.
Slug
A solid, non-skirted airgun projectile (as opposed to a hollow diabolo pellet), typically used in higher-power PCP guns for better long-range performance.
Spring-Piston
A power plant using a coiled steel spring to drive a piston forward on firing, compressing air behind the pellet. The traditional break-barrel design.
Stock
The body of the gun that houses the action and is held against the shoulder, available in wood, synthetic, or adjustable competition styles.
Tank (Carbon Fiber Tank)
A high-pressure air cylinder, commonly rated to 4500 PSI, used to fill a PCP gun's reservoir. See our Tank Fill Calculator to estimate fills per tank.
Tap-Loading (Bolt-Action Loading)
Loading a single pellet directly into the breech via a bolt or tap mechanism, as opposed to a magazine feeding multiple pellets automatically.
Tin
The standard retail container pellets are sold in, typically holding 250 or 500 pellets of a given weight and shape.
Trigger Guard
The loop protecting the trigger from accidental contact, part of basic handling safety on any gun.
Tune
Aftermarket or factory work adjusting a gun's internals, most often to smooth a springer's firing cycle or reduce vibration, sometimes to raise or lower power output.
Under-Lever
A cocking mechanism using a lever hinged under the barrel rather than the barrel itself, common on some spring-piston and PCP repeaters.
Unregulated
See Non-Regulated.
Valve
The component in a PCP or CO2 gun that releases a metered charge of pressurized gas behind the pellet when struck by the hammer.
Velocity
See FPS.
Wadcutter
A pellet with a flat, punch-like nose, cutting a clean hole in paper targets for easy scoring. Sheds velocity faster than a domed pellet, so it's mainly a close-range target pellet.
Windage
The scope adjustment (or holdover) correcting for left-right drift, most commonly caused by wind pushing on the pellet in flight.
Wind Drift
How far a pellet is pushed off its original flight path by crosswind, worse on light, low-BC pellets than on heavier, higher-BC ones.
Wound Channel
The path and cavity a pellet creates passing through tissue, relevant to ethical hunting discussions around adequate energy and penetration for a clean, humane result.
Zero / Zeroing
Adjusting a scope's turrets so point of aim matches point of impact at a chosen distance. Because pellets drop in an arc, a gun is only truly "zeroed" at one specific distance at a time (or two, where the trajectory crosses the line of sight).