Turret following target

I am currently trying to have a turret follow a target. However, it is not rotating properly. As you can see, the barrel does not only rotate around the axis it should, but in the wrong way. It does not align with the rest of the turret.

The turret is supposed to follow the target, rotating the turret and the barrel. Both transforms used seem to rotate properly on their own. However, the pitch transform is a child of the yaw transform, but rotates only around its own x-axis, not aligning with the turrets rotation.

The rotation code:

 public class FollowTarget : MonoBehaviour {
 
     GameObject target;
     public Transform rotTr;
     public Transform targetTr;
     public float upperLimit;
     public float lowerLimit;
     public float speed;
     public bool x;
     public bool y;
 
     // Use this for initialization
     void Start () {
         target = GameObject.FindGameObjectWithTag("Player");
     }
     
     // Update is called once per frame
     void Update () {
         if(target != null)
         {
             if (x)
             {
                 X();
             }
             if (y)
             {
                 Y();
             }
         }
     }
 
     void X()
     {
         Vector3 targetDir = target.transform.position - transform.position;
         // Rotating in 2D Plane...
         targetDir.x = 0.0f;
         targetDir = targetDir.normalized;
 
         Vector3 currentDir = targetTr.forward;
 
         currentDir = Vector3.RotateTowards(currentDir, targetDir, speed * Time.deltaTime / 90, 1.0f);
 
         Quaternion qDir = new Quaternion();
         qDir.SetLookRotation(currentDir, Vector3.up);
         if (qDir.x > upperLimit) qDir.Set(upperLimit, qDir.y, qDir.z, qDir.w);
         if (qDir.x < lowerLimit) qDir.Set(lowerLimit, qDir.y, qDir.z, qDir.w);
         rotTr.rotation = qDir;
         if (rotTr.rotation.x > upperLimit) rotTr.rotation.Set(upperLimit, rotTr.rotation.y, rotTr.rotation.z, rotTr.rotation.w);
         if (rotTr.rotation.x < lowerLimit) rotTr.rotation.Set(lowerLimit, rotTr.rotation.y, rotTr.rotation.z, rotTr.rotation.w);
     }
 
     void Y()
     {
         Vector3 targetDir = target.transform.position - transform.position;
         // Rotating in 2D Plane...
         targetDir.y = 0.0f;
         targetDir = targetDir.normalized;
 
         Vector3 currentDir = rotTr.forward;
 
         currentDir = Vector3.RotateTowards(currentDir, targetDir, speed * Time.deltaTime / 90, 1.0f);
 
         Quaternion qDir = new Quaternion();
         qDir.SetLookRotation(currentDir, Vector3.up);
         rotTr.rotation = qDir;
         if (rotTr.rotation.y > upperLimit) rotTr.rotation.Set(rotTr.rotation.x, upperLimit, rotTr.rotation.z, rotTr.rotation.w);
         if (rotTr.rotation.y < lowerLimit) rotTr.rotation.Set(rotTr.rotation.x, lowerLimit, rotTr.rotation.z, rotTr.rotation.w);
     }
 }