Gun not firing in certain direction

Hello,

So I have my weapon firing but it fires in a forward direction. The gameobject points in the direction I want to fire it but it only goes straight. What am I missing to making the bullet shoot in the direction it faces.

scatterBullet = Instantiate(scatterBulletPrefab, this.transform.position, Quaternion.identity) as GameObject;	
scatterBullet.transform.parent = scatterBulletContainer.transform;
scatterBullet.transform.Rotate(new Vector3(0,0,bulletAngle));
scatterBullet.rigidbody.velocity = (transform.up * 500);

Thank you very much for any help.

If I understand it correctly you already rotated the bullet to the desired angle bulletAngle. So if you only need the bullet to go straight forward in local space use:

scatterBullet.rigidbody.AddForce(scatterBullet.transform.forward * 500f);