GameObject spawnObj = Instantiate(bullet,pos,Quaternion.identity) as GameObject;

Ray ray = cam.ScreenPointToRay(new Vector3(Screen.width / 2, Screen.height / 2, 0));
Debug.DrawRay(ray.origin,ray.direction * 100,Color.red);

using UnityEngine;
using System.Collections;

public class Shoot : MonoBehaviour {
   
  public GameObject BulletStart;
   
  void Update () {
   if(Input.GetKeyDown(KeyCode.Mouse0)){
    /*
    for(int i = 1; i <= 21; i ++){
     Vector3 pos = GameObject.Find(gameObject.name + "/BulletStart").transform.position;
     ToShoot("9x19",pos);
    }
    */
     
   }
  }
  void ToShoot (string bullet_type,Vector3 start_pos) {
   GameObject bullet = Resources.Load("Bullets/" + bullet_type) as GameObject;
   GameObject go = Instantiate(bullet, start_pos, transform.rotation) as GameObject;
   go.rigidbody.AddForce(new Vector3(0,0,-50),ForceMode.Impulse);
  }
  IEnumerator IEShoot()
         {
    for(int i = 1; i <= 21; i ++){
     yield return new WaitForSeconds(0.0001f);
     Vector3 pos = BulletStart.gameObject.transform.position;
     ToShoot("9x19",pos);
    }
         }
  void FixedUpdate (){
   if(Input.GetKeyDown(KeyCode.Mouse0)){
    Vector3 pos = BulletStart.gameObject.transform.position;
    ToShoot("9x19",pos);
   }
  }
}