Every time I test this API, I get absolutely identical results:
First shot – the bullet flies along a ballistic trajectory, and FirearmEffects is called at the right time: t = the time it takes for the bullet to travel a certain distance given air resistance.
Second shot – no effect occurs (not even a visible one), and FirearmEffects is not called.
Third and subsequent shots – FirearmEffects is called immediately in the next frame (1 millisecond), even though the distance the bullet has to travel hasn't changed.
This also holds true for EEHitBy — it is called according to the same principles. The first shot works correctly, but subsequent ones are broken. What's interesting is that the issue is tied to the weapon itself. If you delete the weapon and spawn a new one, the first shot from the new weapon will also work correctly, but the rest will not.