Mirage, environment, bracketing, the wind clock, and how to true your own Gun Number. Back to the calculator.
1. The Mirage Visual Scale
Look through your scope and focus slightly short of the target to see the heat waves in the air.
Speed
Angle
What you see
0 mph
90° (boil)
Waves rise straight up like steam — no horizontal component.
1–3 mph
~60° tilt
Waves tilt diagonally.
4–7 mph
~30° tilt
Waves tilt hard, running across the target frame.
8+ mph
flat
Mirage floats completely horizontal.
Flat is the ceiling. Once mirage goes flat it can't tell you 8 mph from 15 mph — switch to grass or flags at this point.
Glass setup: stay at 12–18x magnification for the clearest mirage at 100–200 yards while keeping enough field of view to transition targets. De-focus your side-focus knob slightly short of the target (e.g. dial to 75–80 yd for a 100 yd target) — the target softens but the air currents in front of it pop.
2. The Environment as a Speed Gauge
No wind flags on the range? Use these baselines.
Speed
Signs
2–3 mph
Faintly felt on your face; leaves twitch slightly.
4–6 mph
Small twigs and light grass move continuously; flags at roughly 45°.
Never guess the exact mph while the timer is ticking — establish a bracket while waiting in the squad line.
Observe the flags for 2 minutes before your turn.
Identify the lull (lowest it drops, e.g. 4 mph) and the gust (highest it kicks up, e.g. 10 mph).
Find your holds for those two exact speeds ahead of time.
Write both holds down before you build your position.
On the clock, it's one decision. Lull hold or gust hold — not a fresh wind call for every shot.
4. The Wind Clock
A clock face laid over the range, 12 pointing downrange, sets how much of the wind actually pushes your bullet sideways.
Where the wind comes from, read on the dial — bold full value at 3/9, mid half value at 1/5/7/11, none at 12/6. Dashed ¾ diagonals are the optional fourth step.
Clock position
Value
Multiplier
12 or 6 (head/tail)
No value
×0
1, 5, 7, 11
Half value
×0.5
3 or 9
Full value
×1.0
A widely-shared version gets this backwards — some sources (including AI-generated answers) label 2/4/8/10 o'clock as half value and 1/5/7/11 as quarter value. That's swapped from what long-range wind-doping instruction actually teaches. Use the table above.
5. How to True Your Hold
Your Gun Number is only as good as the one real hold you build it from. This is the same shortcut long-range and rimfire shooters trade on forums like Sniper's Hide — a rough, fast field check, not a re-run ballistic solve.
Pick a day with steady, measurable wind — read the actual mph with a wind meter at your position. Gusty, variable days make this harder; a day with a consistent breeze is better for a first pass.
Shoot it full value (3 or 9 o'clock) at your reference distance (100 yd is typical for NRL22) — that's the only angle where 100% of the wind speed you're reading applies.
Either shoot with zero wind correction and measure how far the group drifted off center in MIL, or dial/hold increasing correction across a few groups until one centers. Whichever correction centers the group is the trued hold.
Plug range, wind speed, value, and that trued hold into the Gun Number formula below. Round to one decimal.
Check it against a second trued distance — if it's off by more than a click or two there, true that distance on its own rather than trusting one constant past 150–200 yd.
Gun Number = (Range ÷ 100) × Wind(mph) × Value ÷ Hold(MIL)
Yours, not universal. This constant comes from one load, one zero, one elevation — yours. It drifts a couple tenths of a MIL by 200 yd and isn't valid for someone else's rifle or a different bullet/velocity.
Haven't trued one yet? Start with 10 as a generic baseline — the old range/100 × wind ÷ 10 rule many rimfire shooters use as a rough starting constant. Less accurate for your specific rifle/ammo, but usable today. Use the calculator →