How to stop textures flickering

When I instantiate a bullet hole on a cube it starts flickering and this is something that I find unpleasant for my game, but when I instantiate a bullet hole on a rounded surface, like a capsule, it doesn't flicker. So how do I fix this? Here's what I mean: http://videobam.com/LcUNs

Here's my script:

 var Barrel : RaycastHit;
 
 var Cam : Camera;
 
 var BulletHole : GameObject
 
 function Update () {
 
 hitRotation = Quaternion.LookRotation(Barrel.normal, transform.up);    
 
 
 
 }
 
 
 function Shoot () {
 
 if(Physics.Raycast(transform.position, Cam.transform.forward, Barrel, 60)){
 
 yield WaitForSeconds(0.1);
  var newBulletHole = Instantiate(BulletHole, Barrel.point, hitRotation);
        newBulletHole.transform.up = Barrel.normal;
        CurrentAmmo -= 1;
        print("The ammo of the MTAR is " + CurrentAmmo);
        newBulletHole.transform.parent = Barrel.transform;
        
    if(Barrel.transform.tag == "Player"){
    
    Barrel.rigidbody.AddForce(Cam.transform.forward * BulletImpactForce);
        
            }    
            
            if(Barrel.transform.tag == "Detail"){
    
    Barrel.rigidbody.AddForce(Cam.transform.forward * BulletImpactForce);
        
            }  
            
            
            
    
    
        }
 
 
 }