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Setup and camera alignment

Practical guide for getting the camera mounted on the rifle, lined up with the bore, and pointed at the target so the trace and the shot both land in sensible places.

The shape of the problem

The bullet leaves the bore. The camera's optical axis is offset from the bore by however far apart the two are physically (typically a few centimetres above or to the side). Both axes ultimately need to point at the same target, but they don't have to be perfectly parallel. Anything imperfect in the alignment becomes a fixed offset between the trace and the actual point of impact, and the Zero on aim button absorbs that offset.

flowchart LR
    A[Camera<br/>optical axis] -.->|offset| B[Bore axis]
    A --> T[Target]
    B --> T
    style T fill:#2d6cdf,stroke:#1f4f9b,color:#fff

What you actually need:

  1. The camera moves with the rifle (no flex, no slip).
  2. The camera sees the target plainly when you're on aim.
  3. The trace direction matches your aim direction.
  4. The fixed offset between trace and impact is small enough that "Zero on aim" handles it.

Mounting the camera

Where to put it

Two practical positions:

  • On the barrel. A rail clamp or 3D-printed cradle around the barrel near the muzzle. Best line-of-sight to the target. Most affected by barrel heating, recoil flex.
  • On the stock or scope rail. A Picatinny / dovetail rail mount on top of the receiver or under the stock. More stable than barrel mounts, but the camera looks past the bore at a small angle that must be accounted for at the target.
flowchart TB
    subgraph rifle ["Rifle"]
        direction LR
        Stock --- Receiver --- Barrel --- Muzzle
    end
    Camera1[Camera on rail] -.-> Receiver
    Camera2[Camera on barrel] -.-> Muzzle
    Muzzle --> Target

Whichever you choose, the camera should be:

  • Rigid relative to the rifle. A loose mount is the single biggest cause of unexplained trace noise.
  • Roughly above or below the bore rather than off to the side, so the offset is in one axis only and easier to reason about.
  • Aimed forward, with the target near the centre of the frame when you're on aim.

Wiring

Route the USB cable along the stock with cable ties or tape so it can't tug on the camera as the rifle moves. A coiled cable that lifts off the rifle as the muzzle rises will show up in the trace.

Aligning camera to bore

You don't need a laser bore-sight rig. The procedure that works:

  1. Set the rifle up at the firing point in your normal stance.
  2. Aim the rifle at the centre of the target through the iron sights or scope, exactly as you would for a shot. Hold steady.
  3. Look at the live preview from the camera. The target should be somewhere in the central third of the frame.
  4. Adjust the camera mount so the target's centre sits roughly at the centre of the frame at this on-aim position. You don't need pixel-perfect, you just need it not to drift to the edge during a normal hold.
  5. Tighten the mount and check the live preview again. Any movement between "loose" and "tight" tells you the mount has play. Fix that before going further.
sequenceDiagram
    participant U as You
    participant R as Rifle + camera
    participant T as Target
    U->>R: Adopt shooting position
    U->>T: Aim at target centre
    R-->>U: Live preview
    Note over U,R: Target should sit near<br/>frame centre at on-aim
    U->>R: Adjust mount until centred
    U->>R: Tighten and recheck

When you can't get it perfect

You usually can't, and that's fine. The live target image only needs to stay inside the central tracking region during a normal hold (see the Tracking region setting in Preferences). If the on-aim image is slightly off-centre:

  • Off by less than 1/4 of the frame. Leave it. The "Zero on aim" workflow (see below) makes the on-aim point read as (0, 0) so the trace coordinates are correct relative to where the rifle points.
  • Off by more than 1/4 of the frame. The hold motion may push the target outside the tracking region during natural wobble. Either reseat the mount, widen the tracking region in Preferences, or reframe by adjusting the camera angle.
  • Trace direction is opposite to aim. Open Preferences > Camera and toggle the horizontal mirror. A barrel-mounted camera mounted the other way up flips left-right relative to the shooter. The preview makes this obvious.
  • Trace is rotated. Use the Rotation drop-down in Preferences to pick 90, 180, or 270 degrees. This is common when the camera body was clamped sideways for clearance.

Setting the tracking circle diameter

Once the camera is mounted and aligned, the only spatial parameter to set is the diameter of the printed black circle the live tracker measures against. There is no calibration step. Every frame derives the mm/px scale from the detected radius and this diameter, so a small distance change after setting it self-corrects on the next frame.

  1. Print the marker sheet from Tools > Print marker sheet.
  2. Pin it at the target distance, in the same plane the target will sit in.
  3. Open Preferences > Target > Tracking circle and set the diameter to the value you just printed (the marker-sheet dialog updates this automatically when you close it, so this is mostly a sanity check).

The camera-to-bore offset doesn't enter the conversion. The live tracker reports millimetres on the target plane.

Zeroing the trace to your aim

The camera's optical axis isn't the bore axis, so the trace's origin (the centre of the printed circle) usually isn't where the rifle is actually pointing when you're on aim. The "Zero on aim" button in the left column locks the current aim point as the trace's (0, 0) so the trace and shot marks line up with where the rifle is really pointing.

flowchart LR
    Aim[Hold rifle<br/>on target centre] --> Click[Click<br/>Zero on aim]
    Click --> Lock[Current aim point<br/>becomes 0, 0]
    Lock --> Save[Offset saved<br/>across restarts]

Two ways to use it:

  • Zero to your aim. Adopt your shooting position, hold the sights on the target's centre, and press Zero on aim. The trace now reads "where the rifle is pointing relative to the centre of the target". The offset is saved automatically and survives restarts.
  • Zero to a known group. Fire a small group (3 to 5 shots) with the rifle zeroed normally. If the group centre is a few millimetres off the target centre, hold the rifle on the group centre in your natural shooting position and press Zero on aim. Subsequent shots will register relative to where the bullets actually land.

If you ever want to revert the origin to the printed circle's centre (for example if you re-mount the camera), press Clear zero. The button is enabled only while an offset is in effect. The tooltip on Zero on aim shows the current offset value when one is set, so you can sanity check it.

While a zero offset is in force the camera preview adds two visual cues. A small magenta cross marks the chosen zero point on the live frame and tracks the printed circle as the camera moves, and a "Manual zero" badge appears in the bottom-left of the preview. Both disappear once you press Clear zero.

For dry-fire practice the bullet-impact part of the second workflow doesn't apply. Just zero to your aim and the trace will read in "distance from intended aim point" coordinates.

Sanity checks

After setup, before recording sessions:

  • Move the muzzle by a small known amount (a few centimetres at the target plane) and watch the trace move by the same amount.
  • Tap the rifle gently. The trace should jump and then settle, not drift away.
  • Cover the lens. The detector should report tracking lost, not lock onto a different blob.
  • Fire one shot. The shot mark should appear inside the recorded hold zone, not somewhere else entirely.

If any of these fail, revisit the mount before tuning the tracking circle diameter or detector settings.