Guides · Long-range effects

Spin Drift: How Much, From What Range, and When to Ignore It

Spin drift for a 6.5 Creedmoor and a .308 from 100 to 1,200 yards, the range where it passes one click, how twist and stability change it, and why the .308 drifts more than the faster-twist 6.5.

6 min readSolved with the Ballista engineUpdated October 2026

The .308 in this article has the slower twist, 1:10 against the 6.5 Creedmoor’s 1:8. It also drifts more from spin: 13.1 inches at 1,000 yards against 7.4. Twist rate alone doesn’t set spin drift. Stability and time of flight do, and the shorter .308 bullet has more of both.

What spin drift is

A spin-stabilized bullet keeps its nose pointed slightly to one side of its path as the path curves downward. With right-hand twist the nose points a little right, the air pushes on that slightly angled body, and the bullet drifts right. With left-hand twist it drifts left by the same amount. The effect starts small and builds with time in flight.

Litz gives a simple empirical formula for it in Applied Ballistics for Long-Range Shooting. The Ballista engine uses it:

spin drift (in) = 1.25 × (Sg + 1.2) × (time of flight in seconds)^1.83

Sg is the gyroscopic stability factor from Miller’s formula, which depends on bullet weight, length, diameter, twist, velocity and air density. The engine reports it with every solution: 1.63 for the 6.5 and 2.40 for the .308. The .308 bullet is shorter in calibers (4.03 against 5.26), so it’s more stable even in a slower twist. Add its longer flight time, 1.79 s to 1,000 yd against 1.50 s, and it ends up drifting more.

How much, by range

Because spin drift grows faster than range, it can’t be zeroed out. A windage zero at 100 yd takes out 0.02 mil for the 6.5, which leaves almost all of the 0.21 mil at 1,000 yd still to correct.

When it’s below a click

Here are the distances where spin drift first reaches half a click and a full click in MIL, and one quarter-MOA click:

• 6.5 Creedmoor: 0.05 mil at 300 yd, 0.1 mil at 575 yd, 0.25 MOA at 450 yd.
• .308: 0.05 mil at 225 yd, 0.1 mil at 400 yd, 0.25 MOA at 300 yd.

Inside those distances, ignore it. Past them, it belongs in your windage. On a 12-inch plate at 600 yd, the .308’s 3.6 in is not a miss on its own. Added to a wind error on the same side, it can be the part that pushes the shot off the edge.

Another way to size it: at 1,000 yd, spin drift equals a full-value crosswind of 1.1 mph for the 6.5 and 1.2 mph for the .308. That’s less than the edges of a ±1.5 mph wind bracket. The difference is that wind errors scatter both ways while spin drift is always on the same side. Leave it out and every long shot starts with a known bias. It also makes left and right winds unequal, as the wind drift article shows.

Twist and stability

A faster twist raises Sg, and spin drift rises with it, but slowly. The formula uses Sg + 1.2, so going from 1:9 to 1:7 in the 6.5 raises Sg from 1.29 to 2.13 and spin drift at 1,000 yd only from 6.5 to 8.7 in. Twist leaves time of flight alone, and time of flight carries the bigger exponent.

Treat the bottom row of each block as a warning. An Sg near 1 means the bullet is barely stable at the muzzle. A marginally stable bullet may not fly to its published BC, and then drag, not spin drift, becomes the larger error. Pick the twist for stability. Spin drift is only a consequence.

Air changes Sg, and time of flight cancels most of it

Miller’s formula raises Sg in warm, thin air and lowers it in cold, dense air. At 6,000 ft and 20°F (density altitude 4,800 ft) the 6.5’s Sg goes from 1.63 to 1.88. You’d expect more spin drift. The engine gives 7.3 in at 1,000 yd against 7.4 at sea level, because the thinner air also shortens time of flight from 1.50 to 1.42 s. On a 95°F day at sea level it’s 7.4 in. In practice spin drift for a given rifle is close to a constant you can learn for each range.

Left-hand twist

A left-hand barrel drifts the bullet left by exactly the same amount: 7.4 in at 1,000 yd for the 6.5 in a 1:8 left twist. It also reverses the vertical crosswind jump. If you use a calculator, set the twist direction. A left-hand rifle solved as right-hand is off by twice the spin drift, 0.41 mil at 1,000 yd for the 6.5. And in the Northern Hemisphere a right-hand twist adds to the Coriolis drift, which also goes right, while a left-hand twist works against it.

In the app

Ballista solves spin drift with the same formula when the profile has the twist and the bullet’s length. In the profile, “Twist direction” is Right or Left. The Sources sheet, opened by tapping the elevation or wind card, lists the “Spin drift part” of the windage and the “Stability” as an SG value. With no crosswind, the wind card is titled “Spin drift”, because that’s all that’s left in it. Spin drift is on by default; the switch is under Corrections in Settings.

In practice

1. Include spin drift in your windage past about 400 yd for a .308-class load and 600 yd for a 6.5 Creedmoor-class load, or let the solver do it.
2. Learn it as one fixed number per range for each rifle. Weather barely changes it.
3. Remember it’s a bias. Wind from the twist side partly cancels it; wind from the other side adds to it.
4. Choose twist for stability first. Don’t pick a slower twist to reduce spin drift.