Ballistic Calculator 2 — user guide

A free, open-source ballistic calculator for Windows, Linux and macOS, built on Avalonia UI. This is its user guide: how to describe a load, zero it, run it, and read the answer — plus what the numbers mean and where they stop being trustworthy.

Start here

If you…	Read
have never seen this application	What Ballistic Calculator 2 is — what it computes, and what it deliberately does not
want it running	Installation and first run — from the Releases archive to a trajectory on screen
want to compute a shot	Your first trajectory — the six tabs, the imperial/metric choice, and what OK does
are new to external ballistics	Recommended reading — the books and references this guide leans on instead of repeating

Everything else is below, in the full contents.

What this guide is, and what it is not

It documents the application, not ballistics. A concept is explained only where not explaining it would leave part of the interface unusable — what a form factor is, why a drag table beats a ballistic coefficient, why group size has to be entered as a 1σ per-axis figure, station pressure versus sea-level pressure. Everything beyond that is someone else’s book, and better in their hands than ours: see Recommended reading.

It is also organised by task, not by menu. The order follows the work — describe the load, set the conditions, zero it, run it, read the answer — and each step of the Shot Parameters dialog has its own article, written around what you are trying to do rather than walking its fields top to bottom. The exhaustive field-by-field tables live once, in the reference part.

All articles

The guide is being written article by article. Entries that are links are written; plain entries are planned — the structure is listed in full so you can see what is coming and what is missing.

Getting started

• What Ballistic Calculator 2 is — what it computes, what it does not, and the risk notice
• Installation and first run — download to running app, and what it stores where
• Your first trajectory — the imperial/metric choice, the six tabs, pressing OK
• Updating the application — what a new release replaces, what it keeps, and how your presets survive it

Building and running a shot — one article per tab of the Shot Parameters dialog, in tab order

• The Ammunition tab — by hand, from a saved load, from a .drg curve; when diameter and length matter
• The Weather tab — altitude, pressure, temperature, humidity, and station versus sea-level pressure
• The Wind tab — the direction convention, zones along the flight path, and why the first zone does more than the others
• The Rifle tab — sight height, click values, twist direction and rate; sight and barrel presets
• The Zero tab — zero distance, impact offset at zero, and zeroing with a different cartridge, atmosphere or wind than the shot
• The Parameters tab — maximum range and step, shot angle, dialled clicks, and the Coriolis effect
• Reading the table — every column, and the two conventions behind the drop and windage figures
• The chart view — one variable against range, and the two-curve mode that shows the bullet crossing the sight line
• The reticle view — the sight picture, BDC marks, target boxes and moving-target lead
• The summary view — point-blank range, the dead zone, near and far zero, and where the bullet goes subsonic
• Comparing loads — several trajectories on one chart, and what is worth comparing
• Saving and exporting — .trajectory files, and the two CSV formats

Drag models — where accuracy comes from

• Choosing a drag model — what a BC actually is, when G1 misleads, and what the form-factor switch means
• Custom drag tables — a projectile’s own measured curve, and what a .drg does not carry
• Approximating a drag table — from a multi-BC curve, or from measured velocities
• Converting a ballistic coefficient — the G1 ↔ G7 question, and why it is velocity-dependent

Analysis

• Hit probability — building an error budget that is not wishful, and reading the three outputs

Libraries and editors

• Ammunition library and presets — stop re-typing loads, sights and barrels
• The reticle editor — what the separate editor application is for, and its window
  • Reticle size and zero — the coordinate space every element is placed in
  • Reticle elements — the six element types, and what draw order decides
  • Reticle paths — move-to, line-to and arc, for shapes the other types cannot make

How the calculation works — the mathematics, for readers who want to check a number rather than take it on trust

• The ballistic coefficient — the drag law itself, what a BC divides, and why one number cannot describe a bullet at every velocity
• The 3DOF point-mass model — the two forces that are integrated, the frame they are written in, and how the state becomes a row of the table
• The empirical corrections — spin drift, aerodynamic jump and earth rotation: added to the trajectory rather than integrated with it, and why
• Integration modes — Euler against midpoint Runge-Kutta, the internal step, and measured figures for what the choice is worth

Reference

• Units and measurement systems — every unit the app accepts, and the angular-unit choice
• File formats — .drg, ammunition, reticles and the saved shot, by hand
• What the model includes — which effects are computed, which are approximated, which are absent, and the risk notice in full
• Known problems — what is known, what is ours, and what is the platform’s fault
• Release notes — every release, what it contains and what was known to be wrong with it at the time
• Troubleshooting and FAQ — the recurring stumbles, each pointing at the article that explains it
• Recommended reading — the ballistics this guide deliberately does not teach

Before you trust a number

The application simulates a complex physical process with a great many approximations. Results may be used for education and for planning, but must not be treated as a reliable description of how a projectile will actually behave — see the risk notice in full.

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Source, releases and issue tracker: github.com/nikolaygekht/ballistic.calculator.app.avalonia. This guide lives in the docs/ folder of that repository, so it can be read there as plain Markdown as well as here.