Why does the transform don’t move correct?

Hi there, I’m new to Unity and after working through the tanks tutorial I started to modify the tutorial game to get more practice with Unity. My first “small” task is to rotate the tank turret with the mouse. I got this working. Turret and FireTransform follow the mouse cursor. But when I turn the tank with the arrow or aswd keys the FireTransform follows the tank body. I made a small video to demonstrate the behaviour. The first fifteen seconds shows the turret turning with mouse, the rest the FireTransform behaviour when turning the tank with keys.

FireTransform behaviour

Here is the modified code

 using UnityEngine;
 
 public class TankMovement : MonoBehaviour
 {
     public int m_PlayerNumber = 1;
     public float m_Speed = 12f;
     public float m_TurnSpeed = 180f;
     public AudioSource m_MovementAudio;
     public AudioClip m_EngineIdling;
     public AudioClip m_EngineDriving;
     public float m_PitchRange = 0.2f;
 
 
     private string m_MovementAxisName;
     private string m_TurnAxisName;
     private Rigidbody m_Rigidbody;
     private float m_MovementInputValue;
     private float m_TurnInputValue;
     private float m_OriginalPitch;
     private Transform m_TurretTransform;
     private Transform m_FireTransform;
     private Transform m_ChassisTransform;
 
 
 
     private void Awake()
     {
         m_Rigidbody = GetComponent<Rigidbody>();
         FindTurretAndFireTransform();
     }
 
     private void FindTurretAndFireTransform()
     {
 
         Transform[] transforms = GetComponentsInChildren<Transform>();
         foreach (Transform transform in transforms)
         {
             if (transform.tag == "Turret")
                 m_TurretTransform = transform;
 
             if (transform.tag == "FireTransform")
                 m_FireTransform = transform;
 
             if (transform.tag == "Chassis")
                 m_ChassisTransform = transform;
         }
     }
 
     private void OnEnable()
     {
         m_Rigidbody.isKinematic = false;
         m_MovementInputValue = 0f;
         m_TurnInputValue = 0f;
     }
 
 
     private void OnDisable()
     {
         m_Rigidbody.isKinematic = true;
     }
 
 
     private void Start()
     {
         m_MovementAxisName = "Vertical" + m_PlayerNumber;
         m_TurnAxisName = "Horizontal" + m_PlayerNumber;
 
         m_OriginalPitch = m_MovementAudio.pitch;
     }
 
     private void Update()
     {
         // Store the player's input and make sure the audio for the engine is playing.
         m_MovementInputValue = Input.GetAxis(m_MovementAxisName);
         m_TurnInputValue = Input.GetAxis(m_TurnAxisName);
 
         EngineAudio();
     }
 
 
     private void EngineAudio()
     {
         // Play the correct audio clip based on whether or not the tank is moving and what audio is currently playing.
         if (Mathf.Abs(m_MovementInputValue) < 0.1f && Mathf.Abs(m_TurnInputValue) < 0.1f)
         {
             if (m_MovementAudio.clip == m_EngineDriving)
             {
                 m_MovementAudio.clip = m_EngineIdling;
                 m_MovementAudio.pitch = Random.Range(m_OriginalPitch - m_PitchRange, m_OriginalPitch + m_PitchRange);
                 m_MovementAudio.Play();
             }
         }
         else
         {
             if (m_MovementAudio.clip == m_EngineIdling)
             {
                 m_MovementAudio.clip = m_EngineDriving;
                 m_MovementAudio.pitch = Random.Range(m_OriginalPitch - m_PitchRange, m_OriginalPitch + m_PitchRange);
                 m_MovementAudio.Play();
             }
         }
     }
 
 
     private void FixedUpdate()
     {
         // Move and turn the tank.
         Move();
         Turn();
         TurnTurret();
     }
 
 
     private void Move()
     {
         // Adjust the position of the tank based on the player's input.
         Vector3 movement = transform.forward * m_MovementInputValue * m_Speed * Time.deltaTime;
 
         m_Rigidbody.MovePosition(m_Rigidbody.position + movement);
     }
 
 
     private void Turn()
     {
         // Adjust the rotation of the tank based on the player's input.
         float turn = m_TurnInputValue * m_TurnSpeed * Time.deltaTime;
 
         Quaternion turnRotation = Quaternion.Euler(0f, turn, 0f);
         
         m_Rigidbody.MoveRotation(m_Rigidbody.rotation * turnRotation);
        
     }
 
     private void TurnTurret()
     {
         //adjust the turret rotation based on the mouse position
         RaycastHit hit;
         Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         if (Physics.Raycast(ray, out hit))
             if (hit.collider != null)
             {
                 //adjust turret
                 m_TurretTransform.LookAt(new Vector3(hit.point.x, m_TurretTransform.position.y, hit.point.z));
                 
                 //adjust fire transform
                 Vector3 firePosition = m_TurretTransform.forward * 1.35f + m_TurretTransform.up * 1.7f;
 
                 m_FireTransform.localPosition = firePosition;
                 m_FireTransform.rotation = m_TurretTransform.rotation;
                 m_FireTransform.Rotate(350, 0, 0);
             }
     }
 
 }