Plain-language definitions of the terms used in Benchwork Ballistics
A number describing how well a bullet overcomes air resistance compared with a standard reference projectile. Higher is better: the bullet keeps its speed longer.
Why it matters: BC is the single biggest input to drop and wind drift at long range. A BC only means something together with the drag model it was measured against (G1 or G7); a G7 BC is always a smaller number than the G1 BC for the same bullet.
The shape of the standard reference projectile a BC is measured against. G1 is a flat-based bullet from the 1800s; G7 is a long boat-tail bullet much like modern long-range match bullets; RA4 is a .22 LR round-nose bullet.
Why it matters: Most published BCs are G1, which works well for flat-based and hunting bullets. For boat-tail match bullets, a G7 BC stays nearly constant across speeds, so predictions past a few hundred yards are more accurate. For .22 LR, some makers (e.g. ELEY) publish RA4 BCs and others G1. Always enter a BC with the model the manufacturer quotes.
The bullet's speed as it leaves the barrel.
Why it matters: After BC, the most important input. Factory numbers come from long test barrels and are often optimistic; a chronograph reading from your own rifle is far better. An error of 25 fps shows up as several inches at 600 yd.
How much a load's muzzle velocity changes for each degree of temperature, in fps per °F (or m/s per °C).
Why it matters: Powder burns faster when warm, so the same load is slower on a cold morning than on a hot afternoon. Many loads change 1 to 2 fps per °F, which is 30 to 60 fps between a freezing day and a hot one. Chronograph the load at two temperatures at least 10 °F apart and the app works it out; or type a figure you know.
A device that measures bullet velocity, usually a few feet in front of the muzzle.
Why it matters: Your measured velocity is what makes the numbers match your rifle. Record it per load and per muzzle configuration, since a suppressor usually changes velocity.
The distance from the center of the bore to the center of the scope.
Why it matters: The bullet starts below the line of sight and crosses it twice. Sight height sets how far below it starts, which matters most at short range. Typical scoped rifles are 1.5–2.5 in (38–64 mm).
The straight line from your eye through the scope to the target. Path and drop are measured above or below it.
Why it matters: The bullet never flies straight: it rises to cross the line of sight near the muzzle, peaks, and falls back through it at the zero range.
How far the bullet is above (+) or below (−) the line of sight at a given range.
Why it matters: This is what you correct for. The elevation hold is the angle that cancels it.
The range at which the bullet hits where the crosshair points. Some shooters zero slightly high (e.g. 1 in high at 100 yd).
Why it matters: Every other correction is relative to your zero. Common choices are 100 yd / 100 m for precision shooting, or 200 yd for hunting.
The weather and altitude when you zeroed the rifle.
Why it matters: Your zero is only exact in the air you set it in. The app zeroes in those conditions and then flies the bullet in today's, so a change in temperature or altitude shows up correctly in the holds.
1/60 of a degree: about 1.047 in at 100 yd, 10.47 in at 1000 yd.
Why it matters: Many American scopes adjust in ¼ MOA clicks. Holds shown in MOA can be dialed directly on an MOA turret.
1/1000 of a radian: 10 cm at 100 m, 3.6 in at 100 yd.
Why it matters: Common on tactical and European scopes, usually with 0.1 MIL clicks. Match your holds to your reticle and turrets: don't mix MOA holds with a MIL reticle.
The number of turret clicks for a correction, based on your scope's click value (e.g. ¼ MOA or 0.1 MIL).
Why it matters: Lets you dial the solution directly. Check your scope's actual click value: some scopes track slightly differently from their label.
Where the reticle sits in the scope. A first-focal-plane (FFP) reticle grows and shrinks with magnification; a second-focal-plane (SFP) reticle stays the same size.
Why it matters: FFP reticle marks are correct at any magnification. SFP marks are only correct at one power (often maximum); at other powers, holdover marks represent different angles.
How far the rifling travels for one full turn of the bullet, written 1:10 (one turn in 10 in). Most barrels are right-hand twist.
Why it matters: Faster twist (smaller number) spins the bullet faster, which long, heavy bullets need to stay stable. With the bullet's length, it also determines spin drift.
How strongly the bullet's spin keeps it pointed forward, estimated here with the Miller formula from twist, bullet length, weight and air density.
Why it matters: Below about 1.0 the bullet may tumble; below about 1.4 it is marginal and may lose accuracy and BC, especially in cold, dense air.
A small, steadily growing sideways drift caused by the bullet's spin: to the right with right-hand twist.
Why it matters: Negligible at short range, but often 5–15 in at 1000 yd. The app includes it in drift and wind holds when the rifle's twist and the bullet's length are known.
Apparent deflection caused by the Earth rotating while the bullet is in flight. It depends on latitude and the direction you shoot.
Why it matters: A few inches at 1000 yd: in the Northern Hemisphere bullets drift right, and shots fired east hit slightly high (west, slightly low). Only matters for very long range.
How thick the air is, from temperature, pressure, altitude and humidity. Density altitude expresses it as the altitude with the same density in a standard atmosphere.
Why it matters: Thin air (high, hot) means less drag and less drop; thick air (low, cold) means more. Going from sea level to 6,000 ft can cut several MOA of elevation at 1000 yd.
Station pressure is the actual air pressure where you are, as measured by a phone barometer or a Kestrel. Weather reports give pressure adjusted to sea level.
Why it matters: Ballistics needs the actual pressure. If you enter a weather-report value, choose "Sea-level" and set your altitude so the app can convert it. Mixing them up at altitude badly understates drop.
Wind described by where it comes from, as a clock face with the target at 12: 3 o'clock is from your right, 9 from your left, 6 from behind.
Why it matters: A full-value wind (3 or 9) pushes the bullet the most. At 1:30 or 10:30 it has about 70% of the effect; at 12 or 6 there is almost none.
How far the wind pushes the bullet sideways at a given range. Shown in the Drift column along with spin drift.
Why it matters: Usually the biggest source of misses at distance, because wind is hard to read and changes along the path. The hold is shown as L/R.
The angle between the line of sight and horizontal.
Why it matters: Shooting steeply up or down, gravity acts on less of the path, so the bullet hits high if you hold for the straight-line distance. Enter the range your rangefinder reports along the line of sight plus the angle.
Tilting the rifle left or right so the reticle isn't vertical.
Why it matters: Canting turns part of your elevation into sideways error, low and to the side you lean. At long range, a few degrees can mean a miss. A scope level helps.
As the bullet slows toward the speed of sound (about 1,120 fps / 340 m/s at sea level on a standard day), drag changes quickly; below it the bullet is subsonic.
Why it matters: Predictions get less reliable through this zone and some bullets become unstable. The table flags subsonic rows and the graph marks where it happens.
How long the bullet takes to reach a range.
Why it matters: Longer flight gives wind and gravity more time to act. It also tells you how far a moving target travels before the bullet arrives.
The bullet's kinetic energy at a range, from its weight and velocity.
Why it matters: A common guide for ethical hunting ranges; many hunters use a minimum (for example 1,000 ft·lb for deer), though bullet construction and shot placement matter more.
Suppressors and muzzle brakes attached to the barrel. They can change muzzle velocity (suppressors often add 10–40 fps) and shift the point of impact (POI) relative to your zero.
Why it matters: Set one configuration as the one you zeroed with, and give the others their velocity change and measured POI shift. The app then gives correct holds whether the can is on or off.
The first shot from a clean, cold barrel, which can land slightly differently from later shots.
Why it matters: In hunting and many field situations, it's the only shot that counts.