How do I assign the main camera to a variable?

I am trying to assign the main camera to a variable through script. Everything I have tried has either not worked or has an error that I can't find a way around. I want it so that when the prefab is instantiated, the camera is assigned to the variable. script with variable

 using UnityEngine;
 
 public class WeaponScript : MonoBehaviour {
     
 public float weapondamage = 0f;
 public float raycastrange = 0f;
 public float attackrate = 0f;
 public Camera weaponusingcamera; // weapon needs camera to raycast from,
 public ParticleSystem Shootfx;
 
 private float cooldown = 0f;
     
     // Update is called once per frame
     void Update(){
     
        if (Input.GetButton("Fire1") && Time.time >= cooldown) 
        {
            cooldown = Time.time + 1f/attackrate;
            Shoot();
            Shootfx.Play();
        }
         
     }
 //below is irrelevant to question
     void Shoot()
     {
         
         
         RaycastHit hit;
         if (Physics.Raycast(weaponusingcamera.transform.position, weaponusingcamera.transform.forward, out hit, range ))
         {
             Debug.Log(hit.transform.name);
             
             Enemy enemy = hit.transform.GetComponent<Enemy>();
             if (enemy !=null)
             {
                enemy.Deducthp(damage);    
             }
         }
     }
 }

and the script i want to make the camera assign to

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class GunPickup : MonoBehaviour
 {
     // object 1 is weapon on ground and object 2 is weapon prefab
     public GameObject gunpickup;
     public GameObject gunPrefab;
     public GameObject box;
     // below variable is parent of prefab
     public GameObject emptparent; // emptparent is child of main camera
     private GameObject gun;
     // 
     public Camera cam;
     
     void OnTriggerEnter(Collider other)
     {
         gunpickup.SetActive(false);
         box.SetActive(false);
         gun = Instantiate(gunPrefab);
         gun.transform.SetParent(emptparent.transform);
         // above works perfectly at creating prefab, but prefab has no camera set
         //below is failed attempt at setting the camera for the variable in WeaponScript
         GameObject tempObj = GameObject.Find("GunTest");// the object created by the prefab being instantiated
         WeaponScript weaponScript = GetComponent<WeaponScript>();
         weaponScript.weaponusingcamera = cam;
         
         
     }
 }