Raycast origin random

My raycast's origin is randomly moving up and down randomly so my gun script is inconsistent. Can someone help me with this?

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class Fire : MonoBehaviour {

 public float damage = 10f;
 public float range = 100f;
 public GameObject impactEffect;

 public ParticleSystem muzzleflash;

 public Camera fpsCam;

 //Sound
 public AudioSource Pew;
 public void PlayPew() 
 {
 Pew.Play ();
 }

 void Update () 
 {
     if (Input.GetMouseButtonDown(0)) 
     {
         Pew.Play ();
         Shoot();
     }



 }

 void Shoot ()
 {

     RaycastHit hit;
     if (Physics.Raycast(fpsCam.transform.position, fpsCam.transform.forward, out hit, range))
     {
         Debug.Log(hit.transform.name);

         Vector3 forward = transform.TransformDirection(Vector3.forward) * 10;
         Debug.DrawRay(transform.position, forward, Color.green);

         Target target = hit.transform.GetComponent<Target>();
         if (target != null)
         {
             target.TakeDamage(damage);
         }

         GameObject impact = Instantiate(impactEffect, hit.point, Quaternion.LookRotation(hit.normal));
         Destroy(impact, 0.25f);
     }
 }

}