How to check against the object type of an instance

Ok so I have a bullet that is fired out of my space ship and then replaces itself with an explosion when it hits something (2D game so when it passes over an object). The problem is it is also exploding when it hits other bullets and explosions which would be cool option but not what I am looking for right now. So I tried to set it up in my script here:

 #pragma strict
 
 var ProjectileSpeed : float = 10;
 var ProjectileLife    : float = 5;
 var ImpactType : GameObject;
 var owner : GameObject;
 var canHitSelf = false;
 var canHitSplode = false;
 
 
 
 function Start () 
 {
     rigidbody.velocity += transform.forward * (ProjectileSpeed * 10 * GetComponent(Rigidbody).mass);
     
     var locVel = transform.InverseTransformDirection(rigidbody.velocity);
     locVel.x = 0;
     rigidbody.velocity = transform.TransformDirection(locVel);
 }
 
 
 
 function Update () 
 {
     Destroy(gameObject, ProjectileLife);
     
     var HitObject : GameObject;
     
     //create ray from mouse and... yeah actualy I dont know how this works.
     var ray = new Ray (transform.position, Vector3.down);
     
     //Used to store what we hit
     var hitInfo : RaycastHit;
     
     //use ray to find object
     //Physics.Raycast(ray.origin, ray.direction, hitInfo);
     
     if(Physics.Raycast(ray.origin, ray.direction, hitInfo))
     {
         //get the colliders parent which should be our hit object
         HitObject = hitInfo.collider.gameObject;
         
         if(HitObject != owner)
         {
             if(canHitSelf == false && HitObject != gameObject || canHitSelf == true)
             {
                 if(canHitSplode == false && HitObject != ImpactType || canHitSplode == true)
                 {
                     //Create explosion
                     Instantiate(ImpactType, transform.position, transform.rotation);
                     
                     //Get rid of bullet
                     Destroy(gameObject);
                 }
             }
         }
     }
 }

This had no effect. What I think is happening is that the if statement is looking for the specific instance specified rather than the type of object (e.g. bullet and impact), however, I don't know how I would reference the type rather than the instance. I would also rather not have to add more variables if I could help it, for example I am lookig for something along the lines of a "HitObject != ImpactType.ObjectType" but if that simply is not possible I understand.

Thanks in advance for the help.