How do I prevent my original projectile object from being destroyed?

I have a script for a projectile but there are two problems.

1. After the Destroy Timer ends, the actual game object in the scene gets destroyed and I can no longer spawn the item. The thing is, I had a previous projectile script which is exactly the same but for some reason, in the other project which is an older version of Unity, doesn't have the prefab displayed as a game-object so the projectile works fine. Here, I cannot get the game-object to be removed from the hierarchy so it doesn't get destroyed as one.

2. When I fire the projectile before it gets removed from reality, it simply flashes in and out of existence at the spawn point but doesn't actually move.

Here is the code:

using UnityEngine;

public class Projectile : MonoBehaviour { public float speed = 2f;

 //This is our timer until destruction
 public float DestroyTimer = 4f;

 // Update is called once per frame
 void Update()
 {
     transform.Translate(new Vector3(0f, 0f, speed));

     DestroyTimer -= Time.deltaTime;
     if (DestroyTimer <= 0f)
     {
         Destroy(gameObject);
     }
 }

}

This is the code for my PlayerController, which the Projectile script is connected to. The projectile segment is the last one, at the very bottom.

using System.Collections; using System.Collections.Generic; using UnityEngine; using UnityEngine.SceneManagement; using UnityEngine.UI;

public class PlayerControl : MonoBehaviour {

 //We will need to have access to our player itself. 
   
 public Transform Player;
 public Text ScoreCounter;
 public Text HealthCounter;
 public AudioSource healthSound;

 //Ball Projectile
 public GameObject ShotgunPellet;

 //Spawn Location of the ball
 public GameObject PelletSpawn;

 //Let's also create some publically accessible movement values while we're here. 
 public float rotationSpeed = .1f;
 public float movementSpeed = .2f;
 public float jumpForce = 10f;
 public Image PlayerHealth;

 

 int score = 0;

 
 public void AddScore()
 {
     score++;
     ScoreCounter.text = "Score: " + score;

     if (score > PlayerPrefs.GetInt("HighScore"))
     {
         PlayerPrefs.SetInt("HighScore", score);
     }

 }
 // Use this for initialization
 void Start()
 {
     Cursor.lockState = CursorLockMode.Locked;
     HealthCounter.text = "Health: " + startingHealth;
 }

 int health = 5;
 int startingHealth = 5;

 

 void changePlayerHealthBar()
 {
     PlayerHealth.transform.localScale = new
         Vector2((float)((float)health / (float)startingHealth), 1f);
 }
 void OnCollisionEnter(Collision collision)
 {
     if (collision.collider.gameObject.tag == "Health")
     {
         AudioSource sound = Instantiate(healthSound, transform.parent);
         sound.Play();
         health ++;
         HealthCounter.text = "Health: " + health;
         
         
     }
         if (collision.collider.gameObject.tag == "Enemy")
     {
       
         health--;
         HealthCounter.text = "Health: " + health;
         changePlayerHealthBar();
     }
     if (health <= 0)
     {
         Debug.Log("You lose");
         ExitToMenu();
     }
 }
 void ExitToMenu()
 {
     SceneManager.LoadScene("Menu");
 }
 // Update is called once per frame
 void Update()
 {

    
     //Just to get an intro to how this works, we will start by just rotating the player around so they can see more of the screen
     //Since we just want to rotate around while standing straight up, we want to only rotate in the Y-Axis
     //Player.Rotate(0f, rotationSpeed, 0f);
     if (Input.GetKey(KeyCode.W))
     {
         //Move us one movementSpeed into the forward direction
         Player.Translate(0f, 0f, movementSpeed);
     }
     if (Input.GetKey(KeyCode.A))
     {
         //Move us one movementSpeed into the left direction
         Player.Translate(-movementSpeed, 0f, 0f);
     }
     if (Input.GetKey(KeyCode.S))
     {
         //Move us one movementSpeed into the backward direction
         Player.Translate(0f, 0f, -movementSpeed);
     }
     if (Input.GetKey(KeyCode.D))
     {
         //Move us one movementSpeed into the right direction
         Player.Translate(movementSpeed, 0f, 0f);
     }
     if (Input.GetKeyDown(KeyCode.Space) && GetComponent<Rigidbody>().velocity.y > -.3f && GetComponent<Rigidbody>().velocity.y < .3f)
     {
         //This will give us a RigidBody component that is assigned to the same object as this script
         Rigidbody PlayerRigidBody = GetComponent<Rigidbody>();
         PlayerRigidBody.AddForce(0f, jumpForce, 0f);
     }
     Player.Rotate(0f, Input.GetAxis("Mouse X") * rotationSpeed, 0f);

     //GetMouseButtonUp means the left click was released on this frame. This is what we want for a "click" 
     if (Input.GetMouseButtonUp(0))
     {
         //GameObject.Instantiate creates a new "Instance" of the object we pass it, in this case that's our ball
         //By overriding Instantiate we can assign a parent transform for our ball
         GameObject newShotgunPellet = GameObject.Instantiate(ShotgunPellet, PelletSpawn.transform);
         newShotgunPellet.transform.localPosition = Vector3.zero;
         newShotgunPellet.transform.SetParent(transform.parent);
     }
 }

}

Apologies for the massive code wall.