Trigger Detect Bullet Fire
This tutorial will teach you how detect if a bullet passes a volume.
Create a test room. Insert a trigger_detect_bullet_fire mesh entity. If you only want to detect player fire, check the property Player Fire Only.
In the outputs, add the following output:
|My Output||Target Entity||Target Input||Parameter||Delay|
Compile and run your map, and you should have a trigger that, whenever a bullet passes it, it will output OnDetectedBulletFire.