Spin Drift & Coriolis (Long-Range)
Simplified reference estimate for two very-long-range effects. Full solvers (Kestrel, Applied Ballistics) model these more completely.
How this works
Spin drift happens because a spinning bullet's nose very slightly tracks the direction of its own spin as it flies — a right-hand-twist barrel drifts bullets slightly right, regardless of wind. The Litz approximation used here is a widely published simplified formula that estimates this from the bullet's stability factor and time of flight, without needing a full 6-degree-of-freedom simulation.
Coriolis: real, but tiny at hunting ranges
Coriolis deflection comes from the earth rotating underneath a bullet that's in the air long enough for that rotation to matter — it depends on latitude and which direction you're shooting. Both effects genuinely matter to extreme long-range and competition shooters working at 1,000+ yards; full solvers like Kestrel or Applied Ballistics model them with far more precision than this simplified reference.
Frequently asked questions
Do I need to worry about these at typical hunting ranges?
Not usually — both effects are real but tend to amount to well under an inch at ranges under 500 yards, where wind and range-estimation error dominate far more. They matter most for extreme long-range and competition shooting.
Which direction does spin drift push the bullet?
It always drifts in the direction of the bullet's spin — a standard right-hand-twist barrel drifts bullets slightly to the right, regardless of wind conditions.
Is Coriolis the same everywhere on Earth?
No — it depends on latitude and the direction of the shot, which is why both are required inputs. It's strongest at the poles and effectively zero at the equator for a shot fired due north or south.
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