i have an issue where the particle system on the ballista doensnt collide with the game object, and it just goes through it. I have the box collider on the game object but for some reason they dont collide.
Welcome to the community. Check to see if you set the collider to “Is Trigger”. Triggers to not stop objects, they ignore physics and just register that a collider entered another one.
i just checked, and “is Trigger” is not set on.
Hi MJ28,
Welcome to our community! 
Could you please share screenshots of what you did and see in your game in Unity? At the moment, we do not know anything about your game, so it is difficult to help.
How fast are the particles? Maybe you could create a simple cube with a BoxCollider as a non-moveable target. Then make the Ballista shoot that cube. Test different values in your particle system to figure out if there is a value that makes the particles collide.
You could also try to change the Collision Quality value in the Collision module to see if you get the expected result.
also you can add Debug.Log(“it collided”); inside onCollison method, to see if it actually collides.