Clone Scripts Freezes Unity On PlayMode!

I am making a FPS game and the AI just shoot constantly well the game is running. the Ai shoot script has worked for a while but today it freezes unity on play every time! this only happens with the green Ai shoot and not the Yellow Ai shoot script.

GreenAI Shoot Script:

public class GreenGun : MonoBehaviour { public Rigidbody bullet; public int bulletSpeed; public Transform GreenBotBarrel; public float destroySpeed = 0f; public int coolDown;

 // Use this for initialization
 void Start()
 {
     coolDown = 30;
 }

 void SpawnBullet()
 {
     Rigidbody b;
     b = Instantiate(bullet, new Vector3(GreenBotBarrel.position.x, GreenBotBarrel.position.y, GreenBotBarrel.position.z), GreenBotBarrel.rotation) as Rigidbody;
     b.AddForce(b.transform.forward * bulletSpeed);
     coolDown = 10;
 }

 // Update is called once per frame
 void Update()
 {
     coolDown -= 1;
     if (coolDown < 1)
     {
         SpawnBullet();
     }
 }

}

YellowAi Shoot Script: using UnityEngine;

public class YellowGun : MonoBehaviour { public Rigidbody bullet; public int bulletSpeed; public Transform YellowBotBarrel; public float destroySpeed = 0f; public int coolDown;

 // Use this for initialization
 void Start()
 {
     coolDown = 50;
 }

 void SpawnBullet()
 {
     Rigidbody b;
     b = Instantiate(bullet, new Vector3(YellowBotBarrel.position.x, YellowBotBarrel.position.y, YellowBotBarrel.position.z), YellowBotBarrel.rotation) as Rigidbody;
     b.AddForce(b.transform.forward * bulletSpeed);
     coolDown = 45;
 }

 // Update is called once per frame
 void Update()
 {
     coolDown -= 1;
     if (coolDown < 1)
     {
         SpawnBullet();
     }
 }

}

I hope someone has an answer!