Why is this returning false but somewhat true?

So I am working on a script to fire a weapon. I have an if statement: if(Input.GetMouseButton(0) && currentAmmo > 0){ Now if my currentAmmo is 40 and the mouse is held down then the why does the Debug.Log("Stop") get called soon as the game starts and constantly gets called even while I'm holding down left mouse and when I'm not..

The issue with this code is that the muzFX (Muzzle flash) isn't being set active.. However, the audio is. Here is the rest of the code.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 /// <summary>
 ///    This is the Weapon Controller
 /// This script handles controlling the 
 /// current weapon based on the current
 /// weapons profile.
 /// </summary>
 
 public class WeaponController : MonoBehaviour {
 
 
     [Header("Weapon Parameters")]
     [SerializeField]
     private GameObject currentWeapon;
     
     [SerializeField]
     private GameObject hitFX;
 
     [SerializeField]
     private WeaponProfile weaponProfile;
 
     [SerializeField]
     private float currentAmmo;
 
     [SerializeField]
     private GameObject muzFX;
 
     [SerializeField]
     private AudioSource audioSource;
 
     // [Header("AI Settings")]
     // [SerializeField]
     // private AIController ai;
 
     void Start()
     {
         // Chache references
         weaponProfile = currentWeapon.GetComponent<WeaponProfile>();
         audioSource = weaponProfile.soundFX;
 
 
         // muzFX = GameObject.Find("XFlash");
         muzFX.SetActive(false);
 
         // Fill the first magazine and subtract that
         // from the maximum ammo. (This allows running out of ammo)
         currentAmmo = weaponProfile.magCapacity;
         weaponProfile.ammoCapacity -= (int)currentAmmo;
     }
 
     public void FireWeapon(){
 
         // if(!weaponProfile.isMeleeWeapon){
 
         // If we have ammo and we are firing
         // if(currentAmmo >= 0 ){// }
         if(Input.GetMouseButton(0) && currentAmmo > 0){
     
             // Check if we have a muzzle flash selected
             // and set it to active
             if(muzFX != null) {
                 muzFX.SetActive(true);
                 Debug.Log("Show muzzle flash.");
                 if(!audioSource.isPlaying){
                     audioSource.Play();    
                 }
 
                 
                 Debug.Log("Playing audio: " + audioSource);
                 
                 // Reduce current ammo by the weapon profile's firerate
                 Debug.Log("Firing Weapon..");
                 currentAmmo -= 1 * weaponProfile.fireRate * Time.deltaTime;
 
                 // Gather center of screen Ranging from 0f to 1.0f on X/Y Axis
                 // and cast a raycast. Instantiating the hitFX on point of contact.
                 Ray _rayOrigin = Camera.main.ViewportPointToRay(new Vector3(0.5f, 0.5f, 0f));
                 RaycastHit hitInfo;
                 if(Physics.Raycast(_rayOrigin, out hitInfo, Mathf.Infinity)){
                     Debug.Log("Raycast hit: " + hitInfo.transform.name);
                     Instantiate(hitFX, hitInfo.point, Quaternion.LookRotation(hitInfo.normal));
 
                     // if(hitInfo.transform.tag == "AI"){
                     //     ai = hitInfo.transform.GetComponent<AIController>();
                     //     ai.TakeDamage(weaponProfile.damage);
                     //     Debug.Log("Applied: " + weaponProfile.damage + " damage to: " + hitInfo.transform.name);
                     // }
                 }
             }else { Debug.LogError("muzFlash is null");}
         }else { 
             muzFX.SetActive(false);
             Debug.Log("Stop.");
             audioSource.Stop();
         }
         
     } 
 
     public void EnableReload(){
         // [FIX NEEDED]
         // If the magazine is out of ammo, and there is still ammo left
         // reload the clip, subtract that ammo from our max ammo. This isn't 100% accruate
         // and leaves a few bullets unusable. 
         if(currentAmmo <= 0 && weaponProfile.ammoCapacity >= weaponProfile.magCapacity){
             if (Input.GetKeyDown(KeyCode.R))
             {
                 currentAmmo = weaponProfile.magCapacity;
                 weaponProfile.ammoCapacity  -= (int)currentAmmo;
             }
         }
     }
     
 }