Installing GRT and Running Your First Simulation (Part 2)

October 1, 2025

Reloaders, it’s time to put theory into practice! In Part 1, we covered why Gordon’s Reloading Tool (GRT) is such a game-changer. Now we’ll walk you through installing the software and setting up your first simulation — step by step. Accuracy here matters, so follow the order exactly.

Installing GRT — Quick Tips

Download only from the official source. Avoid unofficial mirrors.
Windows users: Use the installer for either the stable or nightly build. If prompted to install .NET or other runtimes, accept and let them run.
Linux users: Follow the distribution-specific steps on the GRT website; you may need extra libraries.
Create a shortcut: Save yourself time by putting GRT on your desktop.
Backup defaults: Before experimenting, copy the default loads folder or export a profile so you can restore it if needed.
Permissions: If you run into file-saving issues, launch GRT once as administrator to set up config files.
Nightly vs stable: Nightly builds include new features but may be less stable. Use stable if you want reliability; nightly if you want the latest tools.

Step-by-Step Setup (Always in This Order)

A — Rifle & Case Basics

Choose calibre. Select the cartridge family you’ll load (e.g., 6.5 Grendel).
Enter case length (after trimming). Trim to your chosen spec and measure before entering.
Measure and enter case volume. Use the water method and record in grains H₂O.
Measure and enter COAL (Cartridge Overall Length). Seat a bullet at your chosen depth, measure, and enter the real OAL.
Measure and enter barrel length. From breech face to muzzle.
Enter gun weight (optional). Adds recoil figures — handy, but not required.
Measure and enter twist rate. E.g., 1:8 in. Important for bullet stability.

Why A first? Geometry and volume define how powder behaves. If these are wrong, nothing else will line up.

B — Projectile

Select your projectile from the dropdown list (or create a custom entry). Confirm weight, diameter, length, and shape.
If you have BC or sectional density values from the manufacturer, enter them for more accurate ballistics.

C — Propellant

Choose your powder from the database or add it manually.
⚠️ WARNING: Only use reliable data — manufacturer sheets, trusted reloading manuals, or verified labs. Never trust random forum posts.
Enter powder name, starting charge (use the published minimum), and other parameters as prompted.

Run Your First Simulation

Create a small loading ladder (3–5 steps around your safe starting load).
Hit Simulate.
Review results:
- Max chamber pressure (Pmax)
- Muzzle velocity
- Burn efficiency
- Barrel time
- Any warnings flagged by GRT
If you see poor efficiency (low burn %, lots of unburnt powder), try a slightly faster powder and re-run.

Quick Interpretation Checklist

✅ Pmax below CIP/SAAMI max? Safe on paper. Still start low and confirm at the range.
✅ Burn efficiency 90–100%? Ideal. Much lower means wasted powder.
✅ Load density ~90–100%? Good. Be careful of compressed loads unless officially documented safe.
⚠️ Pressure curve too steep? Proceed with very small charge increments on the range.

Safety Notes

Always start with published minimum loads and work up carefully.
GRT is a simulation tool — it does not replace chronographing and watching for pressure signs.
Keep a log of your range results and compare to GRT outputs. This makes your personal database stronger and more accurate.