How to read a ladder test with this tool
What this does, and what it does not do
A ladder varies one thing across its rungs (a powder charge, a seating depth, a primer, whatever you chose to test) and fires small groups at each, looking for where the rifle settles down. The hard part is not shooting it; it is reading the result honestly afterwards. This tool takes your measured groups, does the arithmetic that is easy to get wrong by hand, and describes what the numbers show: which rungs repeat, where the spread looks like wind rather than the thing you are testing, and whether the ladder can separate the rungs at all.
It does not suggest a charge, name a rung to load, or rank rungs for you. There is no built-in knowledge of any cartridge, powder or bullet, and it never prints a value you did not type. The optional value on a rung only labels your own rungs and lets the chart space them. Nothing is uploaded, nothing needs a login, and you do not need a chronograph: a ladder read from group size alone is the normal case here, and velocity columns appear only if you enter readings.
What each measurement means
The same explanations sit behind every “?” in the tool. Most people have paper targets and calipers, so each measurement says how to take it that way first, then with an electronic target or a phone app. Want the sheet in your hand at the bench? Print a bench worksheet with the same columns as the group form.
Setting up a test
9 terms
- Ladder
A ladder changes one thing in steps — whatever you decide to test — and keeps everything else as constant as you can. Each step is a rung. You can run several ladders in one test, for example the same thing tested twice, or two different things side by side; give each its own name.
- What this ladder variesOptional
Name the thing you are changing, so the results can be read later. It is yours to choose: this tool does not assume what a ladder tests, and it never suggests a value for it.
- Rung
A rung is one setting of the ladder's variable. Label rungs however you like (1, 2, 3 or A1, A2, A3). Groups with the same ladder and rung label are treated as repeats of the same setting.
- Rung valueOptional
The setting at this rung, as a number or a short label. If every rung has a number, the chart puts them in numeric order along the axis. The tool never fills this in for you.
- Group #
Shooting the same rung more than once is what lets the tool tell a real difference from luck. Number the groups at each rung 1, 2, 3 in the order you shot them. Leave it blank and the tool numbers them for you.
- Shots
The number of shots in the group. Three is common for ladders; five says more about a rung than three does. Groups of different sizes can be compared, but a group with more shots tends to measure larger.
- Session
A session is one trip to the range: its date, distance and conditions. Keep days separate, because wind, light and temperature change, and the tool points out any rung whose groups come from more than one session.
- ConditionsOptional
Anything about the day that could explain a result later. None of it is analyzed; it is kept with your data and exported with it.
- Distance
The distance to the target in yards. Set it once on the session; set it on a single group only if that group was shot at a different distance. Without a distance the tool still works, but cannot convert inches to MOA.
Measuring a group
5 terms
- Group size(C-C, extreme spread)
Group size is the distance between the centers of the two holes that are farthest apart. It is also called extreme spread, or C-C for center to center. It is the one number every scoring method reports, so it is the only measurement the tool requires.
- With calipers: Find the two holes farthest apart. Measure from the outside edge of one to the outside edge of the other, then subtract one bullet diameter (about 0.224″ for a .22-caliber bullet, 0.308″ for a .30). Measuring outside edge to outside edge and subtracting one diameter gives the distance between the hole centers, which is the number the rest of the world reports.
- Electronic target: Most scoring systems show it directly, often labeled group size or extreme spread. Type exactly what the screen shows, fraction and all.
- Phone app: Mark the center of each hole on the photo and set the scale from a known size (a bullet diameter or the target's grid). Use the app's group size or extreme spread figure.
- Group height(vertical spread)Optional
The vertical distance between the centers of the highest and lowest holes. Velocity differences between shots show up mostly as height at longer range, which is why it is worth recording separately from group size.
- With calipers: Measure from the top edge of the highest hole to the bottom edge of the lowest hole, straight up and down, then subtract one bullet diameter (about 0.224″ for a .22-caliber bullet, 0.308″ for a .30). Measuring outside edge to outside edge and subtracting one diameter gives the distance between the hole centers, which is the number the rest of the world reports.
- Electronic target: Usually shown as height or vertical spread.
- Phone app: Use the app's vertical spread or group height figure.
- Group width(horizontal spread)Optional
The horizontal distance between the centers of the leftmost and rightmost holes. Wind moves groups sideways, so width is where a gust usually shows.
- With calipers: Measure from the left edge of the leftmost hole to the right edge of the rightmost hole, straight across, then subtract one bullet diameter (about 0.224″ for a .22-caliber bullet, 0.308″ for a .30). Measuring outside edge to outside edge and subtracting one diameter gives the distance between the hole centers, which is the number the rest of the world reports.
- Electronic target: Usually shown as width or horizontal spread.
- Phone app: Use the app's horizontal spread or group width figure.
- Center offset, left–right(MPI x)Optional
The mean point of impact (MPI) is the average position of every shot in the group: the group's center. The x offset is how far that center sits to the side of your aiming point.
Right of the aiming point is positive, left is negative. Enter what your target shows.
- With calipers: This is hard to do well by hand, which is why it is optional. Measure each hole's center left or right of the aiming point (right +, left −), add them up and divide by the number of shots.
- Electronic target: Most scoring systems report it, often as MPI or group center, with a sign or a left/right label.
- Phone app: Use the app's group center or MPI offset, checking which direction it counts as positive.
- Center offset, up–down(MPI y)Optional
The vertical part of the mean point of impact: how far the group's center sits above or below your aiming point. Across a ladder, a steady climb or drop in this number is the group moving on the target from rung to rung.
Above the aiming point is positive, below is negative. Enter what your target shows.
- With calipers: Hard to do well by hand, and optional. Measure each hole's center above or below the aiming point (up +, down −), add them up and divide by the number of shots.
- Electronic target: Most scoring systems report it, often as MPI or group center, with a sign or an up/down label.
- Phone app: Use the app's group center or MPI offset, checking which direction it counts as positive.
Marking a group
6 terms
- FlyerOptional
Mark a group as having a flyer when one shot went somewhere you can explain: you pulled it, or a gust caught it. The group still counts, because your guess about a flyer can be wrong, but the results footnote it with the cause you chose so you can judge it yourself.
- Compromised targetOptional
A compromised target is not a measurement of what you were testing: another shooter's bullet landed in your group, the target moved or tore, or you lost track of which hole was which. It is left out of every statistic by default and counted in the findings, and you can include it again with a switch.
- Bench observationsOptional
Short notes on how the rifle fed and extracted and what the fired case and primer looked like. Leave them blank when nothing was unusual. These are observations only; reading pressure from brass and primers is unreliable, and if anything looks abnormal, stop and check your published load data.
- VelocitiesOptional
If you ran a chronograph, enter each shot's reading. The results show the average, the extreme spread (fastest minus slowest) and the standard deviation. No chronograph is the normal case, and the tool works fully without one.
- NotesOptional
Free text, kept and exported with the group. Not analyzed.
- Your own fieldsOptional
Add any field you record that the tool doesn't have. It is kept with the group, shown in the results and exported to CSV, but the tool doesn't analyze it: you know what it means, the tool doesn't.
Reading the results
10 terms
- Groups used
Groups at this rung that the statistics use. Compromised targets are not counted unless you include them.
- Average group size(mean C-C)
The average of the group sizes (C-C) at this rung. With one group, it is simply that group's size.
- Largest group
The largest group size at this rung. A rung whose average looks good but whose largest group does not is worth another look.
- Evidence(screening / replicated)
A rung with one usable group is screening evidence: it shows what happened once. A rung with two or more is replicated: the groups can be compared with each other, which is the only way to see how much of a result is luck.
- Agreement
For a replicated rung, agreement is the largest group size minus the smallest. It is a direct look at noise: if two groups of the same thing differ by half an inch, a half-inch difference between rungs means little.
- Signal vs noise
The tool compares the spread of the rung averages (largest minus smallest) with the average agreement of the replicated rungs. If repeat groups disagree as much as the rungs differ, the data cannot rank the rungs. That is a real result, not a failed test: it says the differences are smaller than this test can see.
- MOA(minute of angle, true MOA)
A minute of angle is 1/60 of a degree: 1.047 inches at 100 yards, 2.094 at 200, and so on. This tool uses true MOA. "Shooter's MOA" (exactly 1 inch per 100 yards) is a different, slightly smaller unit; the two differ by about 4.5%.
- Velocity ES and SD(extreme spread, standard deviation)
Extreme spread (ES) is the fastest reading minus the slowest. Standard deviation (SD) describes how far a typical shot sits from the average. Both are unstable over a handful of shots: from a three-shot group they are rough indications, not measurements.
- Flags
The flags column collects what the numbers alone don't show: groups marked with a flyer and its cause, compromised targets that were left out, and bench observations other than normal. Values that look mistyped are listed separately, under the results. A flag is a note for you to judge, not a verdict.
- Transcription check
Some electronic targets display group sizes in sixteenths of an inch. When at least 80% of at least 8 inch values sit on that 1/16″ grid, a value that doesn't is probably a slip in copying it, and the tool flags it for you to check against the screen or photo. Caliper and app readings don't follow a grid, so on Auto the check stays off for them.
Record it your way
Nobody records a test quite the same way, so the tool follows what you shot rather than dictating a format. Add as many sessions as you like: a screening outing, a confirmation weeks later, a check at a different distance, each with its own conditions. Name whatever a ladder varies, in your own words. Use any number of ladders, rungs, groups per rung and shots per group. If you keep your own columns, such as a case lot, a bag position or an electronic target’s extra numbers, add them as fields on a group and they are kept, shown and exported back with the rest. They are never analyzed, because the tool cannot know what they mean.
If a ladder’s rungs have numeric values, such as a jump in thousandths, the chart spaces them by value. Otherwise the rungs are spaced evenly in the order you named them. You can overlay several ladders on one chart; the tool tells you when it has aligned them by rung order instead of by value.
How to enter your data
Type each measurement exactly as your target system or calipers show it: 1 1/8, 3/4, -3/8, or a decimal like 1.125 or 0.483, in inches or millimeters. The tool does the conversion. That matters because converting fractions to decimals by hand, through a lookup table or in your head, is where transcription errors creep in, and one wrong digit in a small ladder can move a rung’s average enough to change the story.
The electronic target this tool was built against displays in steps of one sixteenth of an inch. Calipers and photo apps don’t use a grid at all. So the transcription check turns itself on only when your own data follows a grid, and then it flags any inch value that is off it, next to the field and again in the results, because on that data an off-grid value is far more likely to be a slip than a real reading. Check it against the screen or a photo. You can force the check on or off if you know better. You can enter groups one at a time on a phone at the bench, then download the table as a CSV or import an existing one.
Why two groups per rung
One three-shot group is weak evidence. A tight group can be luck, and a loose one can be a single pulled shot. Firing two groups at each rung lets you check whether a result repeats, and that is the only way to tell a real pattern from a coincidence. The tool tags a rung with one usable group as screening and one with two or more as replicated, so a lone group is never presented with the authority of a repeated one.
Vertical spread against horizontal spread
Powder charge mostly shows up vertically, as changes in velocity move the point of impact up and down, and other things you might vary can move impact vertically too. Wind and hold show up sideways. When most of your groups are wider than they are tall, a large part of what you are measuring is probably not the thing you are testing, and comparing rungs on total group size alone will mislead you. In that case compare rungs on vertical spread as well. The width-against-height chart shows every group as a dot; dots below the dashed line are wider than tall.
Signal versus noise
The most useful check is a simple one. Compare how much the rung averages differ from each other with how much a rung’s own groups disagree with each other. If the rungs differ by less than a single rung disagrees with itself, the ladder cannot rank those rungs, whatever order the averages happen to fall in. That is a real result and a common one, not a failed test. It usually means the differences you were hoping to see are smaller than your rifle, ammunition and the day can resolve in this many shots.
A flyer is not a compromised target
These are different things and the tool treats them differently. A called flyer is a shot you believe went astray, whether from a pulled trigger or a gust. It is still your data, so it stays in the numbers, marked with a note and its cause, because whether it was your mistake or the wind leads to different next steps. A compromised targetis one that is not a measurement of your ammunition at all, for example another shooter’s bullet landing in your group. It is excluded from every statistic by default, and you can include it if you want to see the difference.
Notes for electronic targets
Two fields on some electronic targets are kept as your own columns and shown, but not analyzed. The MBC value appeared to be a radius: across a full session it tracked center-to-center size divided by two almost exactly, so it adds nothing beyond C-C. The “series number” repeated across groups, which suggests it is the score rather than an identifier, so it cannot tell one group from another. Use your own rung and group labels to identify groups. If you import a CSV that includes those columns, the tool keeps them and tells you why they are not used.
Look for a region, not a single group
A single small group is the least trustworthy thing on a ladder. What tends to mean something is a run of adjacent rungs that agree with each other. For each ladder the tool reports the rung with the lowest average group and shows how tightly that rung’s own groups agree, along with the averages of its neighbors. Whether that rung is a narrow notch or part of a wider region is a judgment that depends on your rifle and your wind, and it is left to you. Read the per-rung table across the ladder rather than down to the smallest number.
Go deeper
The method behind this page is taught in the handloading lessons:
- Running a Charge Weight Ladder
- OCW, Ladders and Seating Tests — Which Answers What
- Velocity Statistics — ES, SD, and Their Limits
- Developing a Load Without a Chronograph
The illustrative example uses invented numbers and no charge values. Group sizes are shown in inches; MOA uses true MOA (1.047 inches at 100 yards) and is worked out for each group at its own distance.