Thanks! At the moment the weapon system is intentionally a bit hybrid, because this early version is also helping me understand what feels best for different players.
Picking up ammo can currently switch you to that weapon automatically, but you can also switch manually at any time with the mouse wheel or the number keys 1–5.
Feedback like this is exactly what I’m looking for, though. I may change the behaviour so ammo pickups never force a weapon switch, or make it an option.