Rotation and Velocity of bullets.

Hey you all!

So, I'm working in 2D. I've got a bullet firing from a turret that can rotate. The bullet is supposed to determine its movement vector based on where the mouse was when it was fired -- but I'm having trouble getting the bullet to both rotate in the direction it's going and go in that direction at the same time. Basically, I can have one or the other, but not both -- it's because if I orientate the bullet to its movement direction at all, it changes the angle somehow. So, if I comment out the line that assigns the angle, the bullet moves correctly. But when it's in, the bullets rotate correctly. But they always end up going "down" on the y axis. Here's the function -- what am I doing wrong, do you think?

 public void Shoot(float accuracyVariance, ShotType type) {
         
         if(_currentChargeObject)
             Destroy(_currentChargeObject);
         
         //determine prefab.
         GameObject shotPrefab = _bulletShotPrefab;
         if(type == ShotType.Exploding)
             shotPrefab = _missilePrefab;
         
         //get correct pos.
         Vector3 pos = _bulletStartPoint.transform.position;
         pos.z = _markerCollisionZ.transform.position.z;
         
         
         
         //instantiate.
         GameObject shot = (GameObject) Instantiate(shotPrefab, pos, Quaternion.identity);      
         
         //add velocity.
         Vector3 firingVector = _normalisedMovementVector;
         if(accuracyVariance > 0)
             firingVector = GetFiringVectorWithInaccuracy(accuracyVariance,   _normalisedMovementVector);
         shot.GetComponent<BulletMovementBehavior>().UpdateVelocity(firingVector * _shotSpeed);
         
         //get correct rot.
         Vector3 rot = _bulletStartPoint.transform.eulerAngles;
         rot.z = VectorToATan(_bulletStartPoint.transform.position, _reticle.transform.position);
         shot.transform.eulerAngles = rot;
         //print(firingVector);
         
         
         //bullet behavior.
         if(type == ShotType.Exploding) 
             shot.GetComponent<MissileBehavior>()._explosionPoint = _reticle.transform.position;    
     
         GenerateShell();
             
     }

   
  public float VectorToATan(Vector3 currPos, Vector3 destPos) {
             float opp = currPos.x - destPos.x;
             float adj = currPos.y - destPos.y;
             return Mathf.Rad2Deg * Mathf.Atan2(opp, adj);
             
         }