Ballisto – a basic ballistic computer for target shooting (Android 10+)

Built using Opus 5.5

Ballisto tells you how many clicks to move your sight when you change range from the distance the rifle is zeroed at, and estimates the windage correction either from where the last shot missed or from a crosswind speed.

• Android 10 (API 29) and later, including GrapheneOS and LineageOS.
• Completely offline: the APK requests no permissions at all (no INTERNET, no sensors, no storage), so it cannot connect outside the device.
• Free, no ads, no Google libraries, no third-party code: only the Android framework and the Kotlin standard library (Apache-2.0).
• Designed for 10–100 m smallbore; solves to 3000 m (with falling accuracy beyond ~500 m – see ALGORITHMS.md).

The ballistic algorithms and the source of every drag table are documented in ALGORITHMS.md.

To see the UI on a desktop, open web/index.html in a browser (it then stores the database in the browser's localStorage instead of a file).

Installing the APK

Copy Ballisto-1.0.2.apk, or whatever it is named, to the phone and open it, allowing "Install unknown apps" for the file manager when prompted, or adb install Ballisto-1.0.2.apk.

Using it

1. Welcome – read and tap Next. Exiting here leaves no trace.
2. Ammo – name, bullet weight, muzzle velocity are required. BC (default 0.112) and drag model (default RA4) can be left; you are told when defaults are saved. Grey text = default or example.
3. Rifle – name, click value (default 0.1 MRAD / 0.25 MOA), sight height and zero range are required; twist rate and direction default to 16 / right.
4. Compute – pick rifle and ammo, enter the range you want (shown red while it is still the zero range), choose Miss correction or Crosswind, and tap Compute. The last inputs and result are kept. The rifle remembers the ammo last used with it.
5. Edit Database – spreadsheet view of ammo or rifles; Edit (overwrites, name shown with a grey EDIT: prefix), Copy (new record from a template, name prefixed COPY:), Del, and Delete All, all with warnings.

The database is one plain-text JSON file, ballisto_db.json, in the app's private storage (a .bak of the previous version is kept on every save). It is included in Android backup / device transfer.

Known limitations (honest list)

• No weather input: ICAO standard sea-level atmosphere (15 °C, 1013 hPa).
• No Coriolis, aerodynamic jump, slope angle or head/tail wind.
• Spin drift is a rough estimate (nominal stability Sg = 1.5), applied in Crosswind mode only; twist rate is stored but does not affect it, because the bullet length and calibre needed for a real stability figure are not collected.
• GL drag table is derived from Lowry's 1965 retardation data (see ALGORITHMS.md §3).
• Bullet weight only affects the energy figure; with a G-model BC the path does not depend on it.
• Limited testing, I run it, it works for me.

Licence

App under AGPL-3.0 and/or PolyForm incorporating MIT (see LICENSE). Drag-function data are published reference data from the US Army BRL / E. D. Lowry via JBM Ballistics, credited in ALGORITHMS.md.