OnTriggerEnter not always triggering

For some reason when I fire a projectile (which has Trigger enabled) at my terrain (which is not a trigger) OnTriggerEnter is not being called every time the object hits it.

For example: Dropbox - 2015-03-17-2355-20.flv - Simplify your life

And here is the OnTriggerEnter function (located in the projectile script):

    void OnTriggerEnter(Collider other)
        Debug.Log("enter " + other.gameObject.name);
        if (type == ProjectileType.Player && other.gameObject.tag == "Player")

        if (type == ProjectileType.NPC && other.gameObject.tag == "NPC")

        if (!exploded)
            Debug.Log("explode " + other.gameObject.name);
            exploded = true;
            TerrainController.Instance.GenerateExplosion(rigidBody.position, explosionPower);
            GameObject audio = (GameObject)Instantiate(audioPrefab, rigidBody.position, Quaternion.identity);
            GameObject particalObj = (GameObject)Instantiate(partical, rigidBody.position, Quaternion.identity);
            Destroy(particalObj, 5);
            Destroy(audio, 5);
            if (type == ProjectileType.Player && other.gameObject.tag == "NPC")

There are two possibilities I can think of right now.

  1. You are missing an active rigidbody in the projectile.
  2. The velocity of the projectile is too high for collision detection. You will need to change the collision detection mode in the rigidbody to continuous and make the triggers and colliders much more bigger.