Making a bullet destroy itself on contact.

 using UnityEngine;   
 using System.Collections;
    
 /// <summary>    
 /// This script is attached to the Blaster projectile and it   
 /// governs the behaviour of the projectile.   
 /// </summary>
   
 public class BlasterScript : MonoBehaviour {
   
     //Variables Start___________________________________
     //The explosion effect is attached to this
     //in the inspector             
     public GameObject blasterExplosion;  
     //A quick reference.    
     private Transform myTransform;            
     //The projectiles flight speed.   
     private float projectileSpeed = 10;         
     //Prevent the projectile from causing  
     //further harm once it has hit something.   
     private bool expended = false;
        //A ray projected in front of the projectile    
     //to see if it will hit a recognisable collider.    
     private RaycastHit hit;  
     //The range of that ray.   
     private float range = 1.5f;    
     //The life span of the projectile.    
     private float expireTime = 5;                            
     //Variables End_____________________________________   
     // Use this for initialization   

     void Start ()    
     {  
         myTransform = transform;
         //As soon as the projectile is created start a countdown
         //to destroy it.  
         StartCoroutine(DestroyMyselfAfterSomeTime());
 
     }
 
     // Update is called once per frame
     void Update () 
     {
         //Translate the projectile in the up direction (the pointed
         //end of the projectile).           
         myTransform.Translate(Vector3.up * projectileSpeed * Time.deltaTime);
         //If the ray hits something then execute this code.
         if(Physics.Raycast(myTransform.position,myTransform.up, out hit, range) && expended == false)
         {
             //If the collider has the tag of Floor then..
             if(hit.transform.tag == "Floor")
             {   
                 expended = true;
                 //Instantiate an explosion effect.
                 Instantiate(blasterExplosion, hit.point, Quaternion.identity); 
                 //Make the projectile become invisible.
                 myTransform.renderer.enabled = false;
                 //Destroy the projectile.    
                 Destroy(myTransform.gameObject);   
             }   
         }   
     }
     IEnumerator DestroyMyselfAfterSomeTime()
     {
         //Wait for the timer to count up to the expireTime   
         //and then destroy the projectile. 
         yield return new WaitForSeconds(expireTime);
         Destroy(myTransform.gameObject);
     }    
 }
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

That is the script I am using for my project. It is attached to the projectile GameObject. I use another script to fire the projectile.