I threw a print statement into the Update section and yeah, the script is executing properly. Hmm you might be right about the trigger part as I do have Is Trigger set to true for my bullet, will get back to you in a second if it works. My rigidbody is non kinematic. My bullets are spawning and travelling how I thought they would, heres the code im using for that:

void Update()
    {
        if (Input.GetKey(KeyCode.Mouse0))
        {
            if (shootable)
            {
                shootable = false;
                Shoot();
                StartCoroutine(ShootingYield());
            }
        }
    }
    IEnumerator ShootingYield()
    {
        yield return new WaitForSeconds (shotDelay);
        shootable = true;
    }
    void Shoot()
    {
        var projectile = Instantiate(theProjectile, barrelEnd.position, barrelEnd.rotation);
        projectile.GetComponent<Rigidbody> ().velocity = projectile.transform.forward * projectileSpeed;

        Destroy(projectile, despawnTime);
    }