Top down shooter spreadshot help

How to make a spreading bullet like the ones in shmup games?
I tried to duplicate and rotate the weapon, but it ends up shooting at the same direction.

Here's my code.

Code (CSharp):

1.     void Update ()
2.     {
3.         if ((Input.GetAxisRaw("FireHorizontal") != 0.0f || Input.GetAxisRaw("FireVertical") != 0.0f) && canAttack)
4.         {
5.             Vector3 shootDirection = new Vector3(Input.GetAxis("FireHorizontal"), 0, Input.GetAxis("FireVertical")).normalized;
6.             GameObject bulletInstance = Instantiate(projectile, transform.position, Quaternion.LookRotation(shootDirection)) as GameObject;
7.             bulletInstance.GetComponent<Rigidbody>().AddForce(shootDirection * projectileSpeed, ForceMode.Impulse);
8.             canAttack = false;
9.             Invoke("ProjectileDelay", attackDelay);
10.         }
11.     }
12.    
13.     void ProjectileDelay()
14.     {
15.         canAttack = true;
16.     }

Thanks.

 

I usually have multiple instantiate lines, one for each angle I want the shot to go at.

 

Can you tell me how to set the rotation angle?
It seems like everything i do that doesn't have squiggly lines just ends up shooting at the same direction.

Thanks.

 

Again, I don't do it the most efficient way as angles do my head in. I have extra bullet spawn points that I set to the angle needed then when the player has the multi shot power up I instantiate bullets at each of them at the rotation of the spawn point/s. But.... I focus on 2d so I only have a 2d spread to worry about. The only time I didn't use multi spawn points was when my ship shot in the 4 compass points in which case I used the ships position + vector2.up, down, left, right & found the angles to use to get the 90° increments. I still used 4 instantiate lines tho.