The solver gives you a correction for every distance in the table, and it gives them all with the same confidence. Reality does not work that way: predictions are excellent close in, good in the middle, and progressively less reliable as the bullet slows. This drill finds your own boundary.
What it measures
- How closely predicted elevation matches the elevation that actually works, at each distance.
- Whether the error is a constant offset (a zero or input problem) or grows with distance (a drag or velocity problem).
- The distance beyond which your solution stops being dependable.
Before you start
This drill is worthless on a foundation you have not checked. Confirm all of the following first, or you will spend a hundred rounds measuring a scope height error.
| Check | Why |
|---|---|
| Zero confirmed with five rounds | A zero error is a constant offset on every line of the card |
| Scope height measured, not estimated | Skews the whole trajectory geometry |
| Muzzle velocity measured or trued | The dominant input |
| Drag model matches the coefficient | G1 against a G7 table is invisible up close |
| Click value correct | Turns a good solution into a wrong turret setting |
| A level fitted and used | Cant error grows with dialled elevation |
Setup
| Item | Detail |
|---|---|
| Distances | 200, 300, 400, 500, 600, then continue in 100 m steps |
| Rounds per distance | Three minimum, five if the load allows it |
| Target | Paper with a defined aiming point at every distance — steel tells you nothing about how far you missed |
| Conditions | The calmest day you can find, or a pure head/tail wind |
| Position | Prone off a bipod and rear bag. Remove yourself as a variable |
The drill
- Enter the day's conditionsTemperature, station pressure, altitude. Generate the table before the first shot and write down the predicted correction for each distance.
- Start at 200 mDial the predicted correction. Fire three. Measure the group centre against the aiming point.
- Record the difference, do not correct it yetWrite down what you dialled and where it landed. Resist the urge to chase the impact — you are collecting a curve, not zeroing.
- Step out and repeatSame procedure at each distance. Keep the position, the load and the routine identical.
- Stop when the retained velocity approaches Mach 1.2The solver reports retained velocity per row. Past that point you are measuring transonic behaviour, not your solution.
- Plot the error against distanceThis is the whole point. The shape of the error tells you what is wrong.
Reading the error curve
| Shape | Diagnosis | Fix |
|---|---|---|
| Flat offset at every distance | Zero is off, or the click value is wrong | Re-zero; verify what one click moves |
| Error grows roughly in proportion | Muzzle velocity is wrong | True velocity at mid range |
| Small until 600 m, then grows fast | Ballistic coefficient is wrong | True BC at long range, after velocity |
| Random, no pattern | Data quality — wind, position or too few rounds | Repeat on a calmer day with five rounds per distance |
| Sudden divergence at the far end only | Transonic effects | Not a solver error. Note the distance and stop trusting past it |
This diagnostic is the reason the drill is worth its ammunition. A single confirmed distance tells you that you were right or wrong there; a ladder tells you *why*, and the why is what fixes every other distance at once. The theory behind it is in truing.
Pass mark
You pass when predicted and actual elevation agree, at every distance out to your supersonic limit, to within half of your rifle's group size at that distance. Tighter than that is measuring noise; looser and you cannot expect a first-round hit.
What to log
- Distance, predicted correction, dialled correction, actual impact offset.
- Group size at each distance — your error bar for that row.
- Full conditions: temperature, pressure, altitude, wind.
- Ammunition lot. The whole ladder is only valid for that lot.
Once the ladder agrees, export the confirmed table as a DOPE card and label it with the conditions it was shot in. That card is now data, not a prediction.
Common mistakes
- Correcting at each distance as you go. You end up with six zeros and no curve.
- Shooting it in wind. Vertical is what you are measuring, and a strong head or tail component moves vertical too.
- Three-shot groups treated as precise. They are not; they are a rough centre with a wide error bar. Use five where you can.
- Running the ladder into the transonic region and truing to it. That bakes transonic behaviour into your entire trajectory.
Frequently asked
How much ammunition does this take? +
Roughly 25–40 rounds for a ladder out to 700 m at five rounds per distance, plus a zero confirmation. It is the best-spent box of match ammunition you will shoot all year.
Can I do it in stages across several trips? +
Yes, provided you re-confirm zero at the start of each trip and record the conditions separately for each session. The solver handles differing conditions; an unrecorded zero shift it cannot handle.
What if my range only goes to 300 m? +
Run the ladder to 300 and accept that you have confirmed only that far. Do not extrapolate a card to 800 m from 300 m data — that is precisely the region where an unnoticed error becomes a miss.