Quick answer: Defer the ammo transfer to the completion of the reload animation, and on cancel simply abort without modifying ammo.
If cancelling a reload duplicates or loses ammo, the transfer happens too early. Committing ammo only when the reload finishes fixes the counts. Here is how.
How to fix it
1. Commit ammo on completion
Move rounds from reserve to magazine in the reload-finished callback or animation-end signal, not when the reload starts.
2. Abort cleanly on cancel
If the reload is interrupted, stop the animation and clear the reloading flag without touching magazine or reserve.
3. Guard against double commits
Use a reloading flag so a second reload input cannot start while one is running and the completion handler cannot fire twice.
Catching the ones you can't reproduce
The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.
Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.
This is where a tool like Bugnet earns its place. Its SDK captures every Godot error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.
A crash you can name from its stack trace is a crash you can usually fix in minutes.